Actually quite good...
I got one as an interim device when my iPhone4 when kaput. I'm pretty impressed with it!
I unlocked it for £5 and put my T-mob sim in it, no probs there. If you head over to modaco then there's a fairly active forum there and I was able to root the device easily enough and then proceeded to remove the Voda bloatware. I'm using Holo launcher at the moment, but Launcher Pro made the thing really fast - again impressive at this price.
Something I really like is the RGB LED which works excellently with Light Flow from the play store. Ok, it's not as smooth an experience as the iPhone might have been, but I'm really impressed with what you can get for £100. Also, shove on a Nillkin hard case (again from ebay for less than a tenner) and the whole thing feels much more solid.
I wasn't impressed with the battery at all, however give it a week of charge cycles and it improves hugely.