My iMac had 12GB of RAM and my Air has 8.
However I do still have to manage memory b/c iTunes (always running for Apple TV streaming access) and Safari (at least 5.x) are both RAM hogs. Apparently 6 manages RAM much better. I typically close all tabs, and quit iTunes and Safari on the iMac once or twice a week to reset usage, but I wouldn't call Safari laggy. I don't have Exposer on either machine b/c I couldn't DL it.