I'm pretty happy with mine. The sound quality isn't excellent, but its plenty good enough. You could probably get better sounding headphones (perhaps some that have been mentioned above) for the same price, that may not have the microphone. For example, I have a pair of Marshall Majors, which I use with my iPod, and they sound much better, for about the same price.
The mic works really well, and just slides back up out of the way when you don't need it. The volume control on the cable is great, and also has a mute mic switch which is handy.
The headset is really comfy. I can wear them for ages, even with glasses. My Majors give me a really bad headache after an hour or so, but these are fine. There headset itself has a really short cable, but there's an extension lead if you need to go behind the desk to your PC. I think the cord that is attached to the headset is still a bit short, though. Its a pain to use with an iPod, for example.
As hazeluff said, if you're going to buy these, go for the ones that don't use USB. Then you've got no worries about drivers, and you can use them with anything, rather than just the computer (and maybe PS3/X360?).
Overall, I reckon they're pretty good. If I had to put a number to it it'd be a 7.5/10, I guess.