When my old MacBook died, I was going to replace it with the 11" MBA, but after realizing how limited the HD was and how much it would cost me to get decent storage capacity for my pictures and music I decided to get a 13" MBP.
Yes, I've used the "superdrive" just once since I bought this computer, but I have a healthy amount of storage capacity, an SD slot and heck, I can even play some TF2, L4D 2 and StarCraft 2 (on mid settings) on my free time, for the same price of a 11" MBA with a 128 GB SSD.
I'm in no way a power user, but I like to take my stuff with me at all times. With my games, music, photos and a couple of other programs I have installed I would definitely be short of space with a stock MBA.
Until a ~250 GB SSD from Apple gets a fair price, or the 128 GB becomes the standard drive at just $999, I don't plan on buying a MBA. I like it, a lot, but the base model needs to improve its specs a little bit.