Mines arriving on Wednesday!
One of my mates has got one and he loves it. I've played around with it and it is far better than the Dell X5 and X3i.
You can do tons of stuff with it - games, music, gps, web, tv and all the usual calender, contacts, email etc.
The Ipaq 4150 is almost identical to the 5550 apart from having 64mb RAM, no expansion jackets and no fingerprint reader - could be a better bet if you don't need these features - plus you can get it for around £345 whereas the 5550 is around £430.
What features do you actually need? Personally, I think all of the Ipaq's are better than the equivalents from Dell, Fujitsu, Sony etc. If you don't need the fingerprint reader and jackets, the 4150 is probably the one to go for. If you don't need WLAN, go for a Ipaq 2210 (£300) which also has a CompactFlash slot. For the price, the 4150 is probably the best value - 64mb RAM, 48mb ROM, WLAN, Bluetooth, SD slot and a great screen.
James