firstly, I have to say that this is the best case I've come across for the iphone. I've looked at quite a few and have quite a lot of iphone owning friends who have their own cases - all of which were either too chunky or too fragile. But this seems to be a perfect balance, its thin enough that you dont feel any extra bulk yet strong enough to protect the phone from any minor accidents - one prime example is when I dropped it on the bathroom floor, which is tiled and has already claimed the face on a previous handset, and there wasn't a single mark on the phone or the case - just brilliant!!
The downside is that the white case, which I bought for my white iphone, colours really quickly. If, like me, you keep you phone in your pocket, you need to be very careful of what colour your pockets are. Sounds daft but it seems the white is like a colour magnet and will soak up whatever colour your pocket is. My advise is that if you want white, only wear anything with white pockets. Otherwise, I'd go for black just to be on the safe side!
Apart from the colour aspect, a quality product and definately worth considering if you want a slim case with good protection.
Incipio Feather Case for iPhone 3G/3GS - Black