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 ).
However, my motherboard does not support resource remapping (despite the fact that 64bit OSes are somewhat common), so their address space cuts it down to 3200MB.
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.