In terms of a fun factor, the 11" is really is appealing. But, even though it performs well, it just misses a lot. After awhile, I found that I really craved a bigger screen. That meant my windows desktop got more use. Using my 13", I don't even see a sacrifice. Also, I really use the palmrests on my 13"; on the 11", they're a lot smaller. However, for me, the biggest drawback was the battery's shorter runtime. With the rumors of better battery life (I can't remember the source), the 11" would move up a lot.
If, instead, Apple made a 12" and a 14", I think they would appeal to even more. By reducing the bezel, they could keep the same footprint, but add a solid inch to the screen real estate. For the 11", the difference would be quite noticeable.