Uh, me for one. Cases take away from the innate sexiness and the invisible skins don't feel right. Despite my old 3G's nudity, it didn't gain a scratch last year. If someone as clumsy as me can get away without a case anyone can.
My Macbook Pro also kicks it in the buff and looks flawless.
Have you tried to hold the original iphone without a case? My rubber case was to keep me from dropping the friggin thing so many times. They're too slick. The 3G and 3Gs have a plastic back which has a tackier feel. The cool aluminum of the original just stayed slick.
But seriously, the rubber is a good shock absorber. Sexy is not.