well I can put it this way... right now I have firefox, adium, limeware, itunes, mail activity monitor, and 4 yahoo widgets running... with 512, the computer would really start slowing down now, and I would have to close something to speed it up, because it would get 'annoying' slow on a 'fast' computer... with this setup, I would have about 6 mb of 'free' ram...
right now with 2 gigs, I have all those things mentioned opened and computer is running smooth as ****.... not to mention I ahve 846mb ram 'free' and 738 'inaactive' which is just there for the open apps... os i can prolly run PS right now on top of all this and it would still run decent unless i'm doing some REAL heavy editing with HUGE pictures