Ditto.
Am on an Air with 250Gb, and still contend with space management problems.
I've been relying more and more on Dropbox for that very reason. Selective sync gives me the ability to store only what's necessary on the Air while keeping all files on the Mini in the office. If I'm missing something on the Air, I just go to Dropbox online and download the specific item. Tight, clean, controllable.
The MBAir only has just-so-much space, then :::poof!::: Dead in the water with a maxed out hard drive.
Please, please, please...selective sync, soon. I dearly love Evernote, but can't afford the risk of having it crash my drive.