My recently acquired HTC is easily my most expensive phone so far (I've only owned about 4, but almost contrary to Moore's Law seem to pay more each time I upgrade!). Naturally the mere thought of it acquiring a scratch fills me with dread, so buying a skin for it was a bit of a no-brainer for me. After trusting the positive reviews I'm, like so many others, very pleased with this case.
I suppose it looks a bit cheap upon close inspection, in that you can see seams running along the sides, and some of the openings don't look too neatly cut. But I'm just nitpicking, since as a whole the case looks very nice! The way it covers all of the phone means your handset looks far more presentable than it would with a plastic "case" clipped awkwardly to be back. The skin is a very good fit, all the openings and buttons are aligned perfectly. Ok, the thin sides can be pulled back from the sides of the screen using force but I don't think it's physically possible to prevent this with a soft case. Some people have implied that the fact it covers the front buttons is a negative thing. Personally I think this is a good selling-point! Covering the buttons protects them from dust and grime, and means you can feel slightly less guilty about using them with grubby fingers. Oh, and the case's "buttons" are labelled too so you won't forget which does what.
The only negative impacts the skin has on the phone's usability are:
1. The opening for the heaphone jack is the same diameter as the jack itself, which probably makes it hard to plug in most headphone varieties without altering the case.
2. The optical trackball is indented once you put on the case. It's still comfortable to use, but obviously isn't quite as nice to rub as it was without the case.
3. The case doesn't cover the touchscreen itself but you probably will find your fingers brush it occasionally when accessing the edges of the screen (eg, using a scrollbar). On the plus side, the case will probably extend the life of any screen-protectors you apply by preventing them from peeling at the edges.
The case is approx over a mm thick. Whilst I still wouldn't want to drop my phone on concrete (who would?!?), this skin (combined with a screen-protector) almost entirely cocoons the phone and so gives you the reassurance that you can set the phone on a rough or dirty surface or in your pocket without it getting scratched. I'd definitely recommend it!