Once you go Mac you don't go back
17" mac toter here too. I'm going to pick up the 13" MBA. One thing to consider is that the HD is solid state. The problem with 2 vs 4GB of RAM is that after the ram is full the hard drive is used as a virtual ram, which slows down drastically with spinning disks. Not true with solid state drives, which are almost as fast at the flash ram. So I'd go with the 2GB ram to save money.
I agree with the other poster who complained about the bezel around the screen. This certainly should be fixed.
The perfect trifecta for me would be iPhone, 13" MBA, 17" MBP for travel.