I'm in the same boat; I never used any sort of case for my OG, but the plastic back of the 3GS just won't do. I looked into cases, but the thought of adding bulk to the phone seems unwieldily.kaching said:With the OG iPhone, I kept it naked because the metal backing deflected grime well. But with 3GS now, that plastic backing is even more of a magnet for fingerprints than the screen is, so I'm contemplating some sort of skin. OTOH, it's certainly more slip resistant this way, but I only had 1 or 2 mishaps with the OG phone over two years, so I'm not really concerned overall.
My wife and I ordered skins from Gelaskins and SkinIt for the backs of the phones. We had Gelaskins for our iPods and were very impressed with them; they're high quality and have an ever-so-slightly tacky texture which seems great for the iPhone. SkinIt allowed me to create a custom design, so I created a mostly black skin with a small logo. I'll post impressions as soon as we receive the products.