I'm trying to decide the same thing.
I have to decide between MBA and MB - black. One thing I will do when I go to the Apple Store is run normal routines on the ones in the Store. Such as, restart a MBA, and decide how long it takes to get up and running. I have a few web pages I visit on a regular basis, and they take a long time to load. I want to see how long they take to load with only 2GB of Ram. I also hope the MBA at the Store has a video already loaded on it, so i can see how long it takes to load and if there is any breakup in viewing.
I can live with the small hard drive. I read that anyone buying the MBA should reload the operating system before installing any Applications, and use a "custom" install to keep foreign languages and printer drivers I will never need. My backup drive will have to talk to the MBA, though, through USB, since there's no Firewire port on the MBA.
If you pull the switch, let us know what you think after you've run it through some apps.