I've got 1gb and I could actually use a second - this pc runs uTorrent a lot for downloading stuff, and I do fancy Photoshop and Premiere/After-Effects. Doesn't matter what cpu I've got, those last 2 alone are enough to justify having 4gb in the system, even if it's barely got enough to run it.
Those things are friggin memory hogs - almost as bad as Vista's supposed to be (I say almost because you could always close Photoshop; Vista's hard to close and still be able to use other installed programs ).
I currently have a home desktop that uses 1024MB of ram, currently sufficient to run alot of things which I do not see the reason it needs to update. Currently running windows xp pro on it.
I have two laptops , both uses 2GB the differences is one is running a Windows XP Pro and the other is running a Windows Vista Business Edition.... the system is also different since it from different brand of laptops.
I currently feel that the one on Vista is bloated and ram seems to be fully utilized in a weird way ever since vista introduce the SpeedBoost and ReadyBoost + uses up all your ram for cache... lag alot. I heard that those with 3GB or more will not get any better performance unless they release the service pack 1 which I am still waiting.