Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I've used my iPad 2 for about a month with no back cover, and it's still in perfect condition. I don't treat it roughly, but I don't mollycoddle it either.

A back cover is entirely optional unless you have reason to be concerned about drops or harsh gouges.
 
The problem with those hard cases is eventually some random dirt gets inside the case and sits there causing scratches. A co-worker has a red plastic hard case on her macbook, she took it off awhile back to replace the hard drive and was shocked to see that her macbook was filthy and all sorts of scratched up on the inside of it.

If anything I'd put a wrap on it like the one from Zagg, then put it in a case. That way the metal is still protected but the case will help if you accidentally drop it.

Not necessarily true. I've had my iPhone in an iskin case since I got it 5 months ago and there isn't a scratch on it. Of course I take it out now and then for a good polishing. If the skin is good quality, dirt won't get in. I just ordered an iskin Vu for my new iPad 1 at 50% off from their website; in the meantime when it isn't in use or if I am traveling with it I have a soft Incase sleeve for it.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.