The BS guy at the cell phone accessory kiosk across from the Apple store in the mall told me that the little strips on the inside of the Incase Slider actually scratch your phone when you slide it in and out, so if you like to frequently remove your phone, the Incase is one to avoid, but that's just him trying to sell me his case, so he might be blowing smoke.
I had an incase on mine, but i never removed it, so I don't know if that's true, however, i dropped it several times with zero damage to my iphone. In fact, my last hit was so hard, it actually CRACKED the incase, but my iphone was completely unscathed.
I just got a new 32 gig 3GS black, and I'm on the fence. I kind of like to go NAKED with my iphone in my pocket... but if I drop it one time I'm gonna be screwed!!!!