Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
yes it voids your warranty. no, it is impossible to completely turn your iphone/ipod touch into a brick. there are many methods of restoring a bricked iphone/ipod touch, and at least 1 of them works every time.
 
Technically it voids your warranty, but seeing as nothing will ever go wrong or stop you from being able to restore there's no reason why Apple would know.

So to summarise: No reason you shouldn't do it.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.