I really love the iPhone4 design, very sexy, very....glass.
I have a SGP Crystal screen protector = you cannot tell by touch or sight it is on.
However, though I adore the sexiness of a nekked iP4, I have placed mine within the Mophie Juice Pack case. Yes it adds bulk, but it really does provide great battery duration, it gives the phone a feeling of solidity that makes me unafraid to plunk it down on a desk or countertop and best of all, when I accidentally dropped it from 5' onto concrete. The case cracked a bit and when the phone bounced, there was a small gouge on the back and a nick where it WOULD have hit my camera had it been nekked.
I can still charge the phone with the case and there is nary a dent or crack on my phone. this was the first time I have ever dropped my phone.
There was even a small scrape along the ledge that extends just beyond the face of the phone.
Slim cases are pretty for sure but don't offer much drop protection.
WW