Can I upgrade my MacBook Air's solid state drive to 128 GB?

There is one KEY thing you need to look out for:

After Model A1237, Apple switched the hard drive connector entirely. The Model A1237 hard drive cable has a locking bar that flips toward the rest of the hard drive. The Model A1304 hard drive cable has a locking bar that flips AWAY from the rest of the hard drive. Therefore, hard drives from Model A1237 MacBook Airs will not fit with Model A1304 hard drive cables.

Be sure that that the hard drive you purchase is compatible with your hard drive cable!!!!