I have the new 13 inch Air with 4GB but I'm going to switch to 11 inch. The only thing is, I don't know whether I need 2GB or 4GB. Any time I look at the Activity Monitor it says I'm using over 2GB of RAM, even though I'm not doing that much the MacBook. Am I correct in saying that only the 'Active' memory is actually being used? Though even 1.5GB being used seems like a lot for the few things that I have running.