I use an Otterbox Commuter - whilst I do miss the aesthetics of not using a case, I am very precious about my gadgets and absolutely can't stand dings & scratches. I'm glad I did go for the Otterbox - I use my iPad every day and take it on the road to uni for study... it gets handled a lot. I checked the case and screen protector the other day and noticed all sorts of dings and scrapes - all of which would have scarred it otherwise. I know it's personal preference and all, but after spending the money on it I'd be gutted to have it bruised. I made the mistake of not using a very good case for my old 3GS and it got punished pretty quickly. Now my iP4 has an Otterbox Defender and it's fantastic to remove it from the case every once in a while to see the iP4 as shiny as it was on launch day. I guess I may be being too precious, but it gives me joy to keep my stuff pristine, so that to me is a greater pleasure than using it ever day and after a while watching it get battered by my own carelessness.
Plus, everyone wants to play with an iPad - it's like pass the bleedin' parcel at times and not everyone understands how or cares to look after stuff, so a good case puts my mind at rest.
Each to their own I guess!