I have about 15 cases, all the way from a true carbon fiber DRO concepts covers to many bookcase portenzo type cases. I think my Zum/Poly/icarbons smart cover is about the best combo I own. I travel for a living and make about 10 flights/hotels a month.
1. the smartcover is the most thin, precision cover I own. fits perfectly and is handy in all situations. Both cover and zum fit precisely.
2. the Zum protects the back and locks cover on. Also very easy to take off without "wearing" edges so long term the fit suffers. I have this in a lot of other cases/covers - take them out every day, and the "nubs" or whatever holds it in, wear down. Not so with Zum.
3. the combo of the two lets the ipad slide in an out of my timbuk2/waterfield bags better than other bulky or sticky cases. This is huge when you are retrieving from under air seats.
I'm done buying until the ipad3. I need to garage sale my other cases...