I recently got an 11" air, and honestly can't see the need for a 13 or a 15". The latter would, in my opinion, stop being an "Air" and be more of a "brick" in terms of weight and size. The beauty of the MBA (ok, one of the beauties) is its portability.

I have to admit, though, choosing the 11" didn't come easily. I knew I wanted it for its compactness, but I was convinced the screen would be too small.

Do yourself the favor and challenge your assumptions. Go play with it. Especially play with it using Lion and its full-screen mode for apps like Safari and Mail. This is where the Air really shines.

To me the only benefit to the 13" is the larger battery. Otherwise the 11" is perfect.