I have 3gb in mine and I cant see any difference for day-to-day stuff between that and 1gb. Wont be long till we need 4gb though.
I still run XP though. I have Vista dual-booting but I only ever use it to test DirectX 10 stuff, so I'm not all that familiar with how much memory it uses.
Anything I have read recently seems to think that 2gb is just about the sweet spot at the moment...but memory is one of those things that you cant get enough of. And its cheap.
The greatest delight is to mark one's enemy, prepare everything, avenge oneself thoroughly, and then go to sleep.