A family member bought one 40" and I've had a play around on it. I own a 37" EX723 2011 series Sony and had a 2010 32" EX523, so my starting points. Its a nice set, picture is good once setup correctly with all the usual Sony features. Focusing on things I missed or found different, the XMB menu is a bit slower than my current model (maybe a slower cpu?) not that it really affects the use of the tv its just not a smooth or quick but this is very very minor. Only other thing I really noticed is you get very basic control over motion flow (100mhz etc) compared to my current and previous set. That would annoy me a little as I didn't enjoy the default setting but again its minor stuff. I've seen the 2012 HX753 series in store next to the EX653, given the choice I'd get the HX, its using a better panel and the picture on same setup looks better but I know its more expensive. Basically two minor niggles on the EX653, it wouldn't put me off buying one if in budget but if I could afford and was buying now I'd get a HX series. Overall I like XMB, the online services like iPlayer etc are good, media interface (see Serviio below) is very family friendly i.e easy to use. All the reasons I recommened the EX653 to my relative and still think it was a good purchage for the,
Oh and on Sky SD the bravia engine once you change the defaults does a fantastic job imo on making the picture look good. Low bitrate, low res channel (Viva? etc) it rescues them as best it can! Sound on the 40" was good and massive improvement on Samsung 32" in replaced, don't know about other sizes. Its not reflective screen particulary but depends on your setup and lighting to some extent.
If you want to use it to play back music, video, pictures from your PC I'd recomment Serviio. Its free, available for Windows, Mac, Linux and supports Sony very well. Sony does its own version called Homestream, same basic application just with Sony branding.