I'm quite frankly shocked and appalled! 
Well anyway, I'll be the first to mention it. OK, I know it's a Shuttle which doesn't necessarily give you the flexibility you'd get with a self-build HTPC but look at the features:
Chassis
G5M-type aluminum chassis (black)
Mirror front face with golden finish
Integrated VFD Media Display (Versatile front-panel display)
Storage bays: 1 x 5.25", 2 x 3.5" (1 internal)
Dimensions: 31 x 20 x 18.5 cm (LWH),
Weight: 3.3 kg net / 4.6 kg gross
VFD Display and Remote Control
Versatile Front-panel Display (VFD) shows helpful information like
Date and time, CD track and title, TV channel, DVD title and progress and more
Integrated receiver for remote control
Shuttle multimedia remote control
Compatible with Windows Media Center (Vista or MCE 2005)
Mainboard
Shuttle FG33, Shuttle form factor, Dimensions: 25.4 x 18.5 cm
proprietary mainboard design for Shuttle XPC Barebone SG33G5M
Chipset: Intel G33 Express (Bearlake-G) + ICH9DH
Solid Capacitors for excellent heat resistance for enhanced system durability
Color slots/connectors design (Power switch, USB, PCIe, PCI)
Power supply
250 Watt mini power supply unit
Input voltage range: 100~240V
Connectors: 20-pin ATX, 4-pin ATX12V
Dimensions: 190 (L) x 82 (W) x 43 (H) mm
EMI certified: FCC, CE, CCC
Safety certified: TÜV, UL, CB, CCC, CSA, NEMKO
Active PFC (Power Factor Correction)
Power plug region specific
Processor support
Socket 775 supports Single/Dual/Quad Core processors from Intel
with Core technology (65nm) and 800, 1066 or 1333MHz front side bus:
Core 2 Quad Q6xxx, Core 2 Duo E6xxx / E4xxx,
Pentium Dual-Core 2xxx and Celeron D 4xx series.
Designed for the upcoming Intel 45nm Core 2 multi-core processors.
Supports Pentium 4/D processors at 800MHz FSB.
Processors with 533MHz FSB are not supported.
Please refer the support list for detailed processor support information.
Overclocking
Overclocking settings:
CPU frequency, CPU voltage, RAM frequency, RAM voltage
Dynamic Overclock feature:
Easily overclock from 3/5/7/10/15/20% through the BIOS.
Processor cooling
Shuttle I.C.E. 2 (Integrated Cooling Engine)
advanced I.C.E. 2 Heatpipe technology, linear controlled 92mm fan
SilentX cooling and noise reduction technology with Active Airflow
Memory support
2x 240 pin slots, supports Dual Channel
supports DDR2-667/800 SDRAM memory
(up to DDR2-1066 in overclocking mode*)
up to a total size of 4 GB, max. 2 GB per DIMM
Slots
1x PCI-Express (16X) supports 8 GB/s data transfer
1x PCI (32 bit)
Integrated Graphics
Intel Graphics Media Accelerator 3100 (GMA 3100)
Full Windows Vista Aero experience
Intel Clear Video Technology
Hardware acceleration for MPEG2 and VC1 content
DirectX 9.0 support, Shader 3.0
Dynamic Video Memory Technology (DVMT) 3.0
Shared Memory size up to 384MB
HDMI connector (High Definition Multimedia Interface)
supports HDCP (High-bandwith Digital Content Protection)
transmits SPDIF digital audio signals
DVI adapter included
VGA connector for analog displays
Dual monitor operating possible (1x digital over HDMI/DVI plus 1x analog over Sub-D)
8-channel audio with DD/DTS
7.1 channel High Definition Audio, Realtek ALC888DD codec
Supports Dolby® Digital Live! and DTS Connect (Digital Theater Systems)
Analog: line-out (8-ch), line-in, microphone
Digital: optical S/PDIF output (digital audio), optional S/PDIF input
Gigabit LAN Controller
Marvell 88E8056 Ethernet network controller (Gigabit)
Supports 100 / 1.000 MBit/s operation
Supports Wake-on-LAN (WOL)
Firewire Controller
Firewire controller VIA VT6308
IEEE1394 OHCI rev 1.0 compliant
with 2 Firewire connectors (front and rear)
supports 400Mb/s, 200Mb/s, 100Mb/s data transfer rate
Drive connectors
3x Serial-ATA II, 3 Gbit/s (300 MB/s) bandwidth, NCQ support
2x External Serial-ATA, 3 Gbit/s (eSATA)
1x IDE ATA 100 drives
1x floppy disk drive
Front Panel connectors
Microphone
Headphone (Line-out)
2x USB 2.0
Firewire (Mini 4 pin connector)
Power button
Reset button
Power indicator (blue LED)
HDD indicator (orange LED)
Back Panel connectors
HDMI (DVI adapter included)
D-sub VGA (analog)
4x USB 2.0
GigaBit LAN (RJ45)
IEEE1394 Firewire (6 pin)
2x External Serial ATA port (eSATA)
Optical S/PDIF output (Digital Audio)
8-ch Audio line-out (2x rear/front, bass/center, surround/back)
Audio Line-in
CMOS button
optional Wireless LAN module (PN18)
optional parallel port (PC8)
Other connectors
2x fan connectors (4 pin)
4x USB 2.0 (two sets with 2x5 pins)
Accessories
Remote Control (compatible with Windows Media Center)
Multi-language user guide,
Driver CDROMs (Windows Vista, Windows XP 32/64 bit)
I.C.E. heat-pipe module,
Cable for FDD, Serial ATA (1x), Parallel ATA (1x)
Power cord,
Screws, Heatsink Compound
From here: http://eu.shuttle.com/en/DesktopDefault.aspx/tabid-72/170_read-14213/
I think the thing that swung it for me was support for 1333MHz FSB (a computer spends 90% of it's time moving data to and from memory btw, so the faster the FSB the better), quad core C2D CPUs, HDMI and Vista 64-bit drivers.
Not the mention the price: £239
from Komplett http://www.komplett.co.uk/k/ki.aspx?sku=338645
A no-brainer? Seems like it to me!
Well anyway, I'll be the first to mention it. OK, I know it's a Shuttle which doesn't necessarily give you the flexibility you'd get with a self-build HTPC but look at the features:
Chassis
G5M-type aluminum chassis (black)
Mirror front face with golden finish
Integrated VFD Media Display (Versatile front-panel display)
Storage bays: 1 x 5.25", 2 x 3.5" (1 internal)
Dimensions: 31 x 20 x 18.5 cm (LWH),
Weight: 3.3 kg net / 4.6 kg gross
VFD Display and Remote Control
Versatile Front-panel Display (VFD) shows helpful information like
Date and time, CD track and title, TV channel, DVD title and progress and more
Integrated receiver for remote control
Shuttle multimedia remote control
Compatible with Windows Media Center (Vista or MCE 2005)
Mainboard
Shuttle FG33, Shuttle form factor, Dimensions: 25.4 x 18.5 cm
proprietary mainboard design for Shuttle XPC Barebone SG33G5M
Chipset: Intel G33 Express (Bearlake-G) + ICH9DH
Solid Capacitors for excellent heat resistance for enhanced system durability
Color slots/connectors design (Power switch, USB, PCIe, PCI)
Power supply
250 Watt mini power supply unit
Input voltage range: 100~240V
Connectors: 20-pin ATX, 4-pin ATX12V
Dimensions: 190 (L) x 82 (W) x 43 (H) mm
EMI certified: FCC, CE, CCC
Safety certified: TÜV, UL, CB, CCC, CSA, NEMKO
Active PFC (Power Factor Correction)
Power plug region specific
Processor support
Socket 775 supports Single/Dual/Quad Core processors from Intel
with Core technology (65nm) and 800, 1066 or 1333MHz front side bus:
Core 2 Quad Q6xxx, Core 2 Duo E6xxx / E4xxx,
Pentium Dual-Core 2xxx and Celeron D 4xx series.
Designed for the upcoming Intel 45nm Core 2 multi-core processors.
Supports Pentium 4/D processors at 800MHz FSB.
Processors with 533MHz FSB are not supported.
Please refer the support list for detailed processor support information.
Overclocking
Overclocking settings:
CPU frequency, CPU voltage, RAM frequency, RAM voltage
Dynamic Overclock feature:
Easily overclock from 3/5/7/10/15/20% through the BIOS.
Processor cooling
Shuttle I.C.E. 2 (Integrated Cooling Engine)
advanced I.C.E. 2 Heatpipe technology, linear controlled 92mm fan
SilentX cooling and noise reduction technology with Active Airflow
Memory support
2x 240 pin slots, supports Dual Channel
supports DDR2-667/800 SDRAM memory
(up to DDR2-1066 in overclocking mode*)
up to a total size of 4 GB, max. 2 GB per DIMM
Slots
1x PCI-Express (16X) supports 8 GB/s data transfer
1x PCI (32 bit)
Integrated Graphics
Intel Graphics Media Accelerator 3100 (GMA 3100)
Full Windows Vista Aero experience
Intel Clear Video Technology
Hardware acceleration for MPEG2 and VC1 content
DirectX 9.0 support, Shader 3.0
Dynamic Video Memory Technology (DVMT) 3.0
Shared Memory size up to 384MB
HDMI connector (High Definition Multimedia Interface)
supports HDCP (High-bandwith Digital Content Protection)
transmits SPDIF digital audio signals
DVI adapter included
VGA connector for analog displays
Dual monitor operating possible (1x digital over HDMI/DVI plus 1x analog over Sub-D)
8-channel audio with DD/DTS
7.1 channel High Definition Audio, Realtek ALC888DD codec
Supports Dolby® Digital Live! and DTS Connect (Digital Theater Systems)
Analog: line-out (8-ch), line-in, microphone
Digital: optical S/PDIF output (digital audio), optional S/PDIF input
Gigabit LAN Controller
Marvell 88E8056 Ethernet network controller (Gigabit)
Supports 100 / 1.000 MBit/s operation
Supports Wake-on-LAN (WOL)
Firewire Controller
Firewire controller VIA VT6308
IEEE1394 OHCI rev 1.0 compliant
with 2 Firewire connectors (front and rear)
supports 400Mb/s, 200Mb/s, 100Mb/s data transfer rate
Drive connectors
3x Serial-ATA II, 3 Gbit/s (300 MB/s) bandwidth, NCQ support
2x External Serial-ATA, 3 Gbit/s (eSATA)
1x IDE ATA 100 drives
1x floppy disk drive
Front Panel connectors
Microphone
Headphone (Line-out)
2x USB 2.0
Firewire (Mini 4 pin connector)
Power button
Reset button
Power indicator (blue LED)
HDD indicator (orange LED)
Back Panel connectors
HDMI (DVI adapter included)
D-sub VGA (analog)
4x USB 2.0
GigaBit LAN (RJ45)
IEEE1394 Firewire (6 pin)
2x External Serial ATA port (eSATA)
Optical S/PDIF output (Digital Audio)
8-ch Audio line-out (2x rear/front, bass/center, surround/back)
Audio Line-in
CMOS button
optional Wireless LAN module (PN18)
optional parallel port (PC8)
Other connectors
2x fan connectors (4 pin)
4x USB 2.0 (two sets with 2x5 pins)
Accessories
Remote Control (compatible with Windows Media Center)
Multi-language user guide,
Driver CDROMs (Windows Vista, Windows XP 32/64 bit)
I.C.E. heat-pipe module,
Cable for FDD, Serial ATA (1x), Parallel ATA (1x)
Power cord,
Screws, Heatsink Compound
From here: http://eu.shuttle.com/en/DesktopDefault.aspx/tabid-72/170_read-14213/
I think the thing that swung it for me was support for 1333MHz FSB (a computer spends 90% of it's time moving data to and from memory btw, so the faster the FSB the better), quad core C2D CPUs, HDMI and Vista 64-bit drivers.
Not the mention the price: £239
A no-brainer? Seems like it to me!