I'm with the OP. I really don't understand this either. Sure, everyone's worried about scratching their phone, but Apple designed it to be beautiful, thin, and pleasurable to hold naked. You're definitely ruining the overall user experience by covering up your iPhone with layers of cheap crap.
I left my 3G completely naked the whole time. Obviously I had scratches, but I still sold it just about a month ago for $300. That's not bad. Sure, if it was mint, I'd probably sell it for about $50 more, but who cares? I had the pleasure of using my iPhone the way it's designed to be used. I didn't have to carry extra crap around that made my phone fatter and heavier.