Not to mention that the 13" MBA has the SD Card slot, which for some is very important.
I guess it depends on what your personal preferences are. I'm much more likely to store documents in the cloud or on a USB stick. My university and work computers all have USB ports, but none of them have SD ports. Plus, my only camera is my iPhone, so no SD card there. The only items that I own that have SD slots and no USB are Wii and DSi, and I can't even think of any reason why I would want to move anything from them to my computer.
Granted, a lot of people do use SD cards, so for them it's one less adapter to carry around. I just don't see myself using it much.
I think the 13" is great with the increased resolution.
4GB of RAM is a must.
1. Wait for the back to school special, free iPod Touch.
2. Then you should wait for the Lion release, might as well have the latest software.
3. The MBA will probably be updated soon after that, so wait for the Sandybridge update. Buy the new one, or discounted old one.
I'm planning to wait for the back to school sale, but I already started summer classes and I'm debating whether I should just get a refurbished one right now.
Even if I'm able to sell the iPod for full price, the refurbished model would only be about $50 cheaper. Having to wait two weeks, having to pay more upfront, having to wait for the iPod rebate and having to sell the iPod to someone all sounds like a lot of extra work.
if you don't need a computer until the fall, there are plenty of good reasons to wait.