As someone finishing grad school, I wish the 13"MBA was around last year. It would have been the perfect choice.
It was interesting to watch students, myself included sometimes, arrive to class early and pick their seats according to the locations of power outlets. Students with newer MBPs never had to worry.
Depending on your studies, the 1440x900 resolution of the 13" MBA may make a difference. I know I craved more than 1280x800, especially for working in Excel. I couldn't or wouldn't justify spending $1700 + tax just to have a Mac with 1440x900 screen res. Now that option is finally $1250 for students.
Interesting observing the computers used by my classmates in a full time MBA program. It was pretty evenly split between Mac and PC users. Mac users had 13" MB and MBP as well as 15" MBP. PC users had 14"-17" laptops with all but 1 17" being 1440x900, the same as the 15" MBP. Also, only one netbook user which means business students don't see the value in netbooks. Especially since the ribbon UI in MS Office takes up a significant portion of the screen of a 1024x600 netbook. 4+ iPads in our class. That doesn't reflect well on the netbook market.
We also had several students switch from old PCs to 13" MBPs.
Just my observations, and I'll probably pick up a 13" MBA soon