Ideas for securing a MacBook Air?
It is so light, I just rarely need to leave it unsupervised. I'll hand it to the staff to set behind the counter if I need to leave to feed a meter or use the facilities on the rare occasion when I don't have a shoulder bag. 

They are so light and thin, it's not a hassle carrying it. 

If you must, audible alarms that plug into USB ports are available, but who wants to be the guy with the alarm going off unintentionally? Not recommended. 

I would bet Kensington comes out with a leash that goes around the display hinge and tightens before college starts in the fall.