After purchasing my iPhone 3G, I spent several hours searching high and low for a suitable iPhone skin that wasn't a ridiculously tacky-looking, bulky leather case. All that I've found that made me happy is this one.
The original silicone skin I bought was at the AT&T store (along with my iPhone) and they charged me $20 for a thin, crappy skin that was junk. I threw it out, and bought this instead. This skin is cheaper and better than anything else I've found. Perfect fit, looks very cool and unique. Everyone who sees it says, "wow, tire tracks! Cool!"
Here's my one complaint--the hole in the top for plugging in your auxiliary cable or headphones isn't big enough. It's just not cut wide enough. You can press your auxiliary cable in pretty hard, and it will fit, but it squashes the top of the skin in doing so. (No big deal, it just makes it look funny and eventually stretches it, making it looser). Just an annoyance at this point, but I wish they had made it wider.