Did not use a case for my 3GS. And I know that my new 4S is really a looker. BUT...after nearly dropping the new phone twice in just one day, I got myself back to the AT&T store and got an Otter Box Commuter case (with a coupon for 30% off). Also added a clear screen protector. Phone still looks great, and I feel a lot more secure. And the Commuter is not nearly as bulky as some other Otter Boxes I've seen.
Also, I declined Apple Care+ when it was offered to me yesterday. Just didn't think it was worth it, with all the "not covered" clauses.