Meh, it all depends. I have 256 and I'm unsatisfied, although if I'm just browsing the net and messaging/email, it's plenty. I'd like to have 768MB or 1GB so that I could have most everything cached at the same time and not have it re-cached every time I switch a number of programs.
For example, let's say I have IE (say 5-6 instances), ICQ, MSN, KaZaA, Norton 2k2, AnalogX POW!, and winamp open. All that is fine and they don't need to HD-crunch at all if I close/open any of those. But say I go to a game like Wolf, and then go back. Well everything needs to crunch again (ie, re-cache). It'd be real nice if I could have everything I used all the time, able to open/close/re-open and not have to hear HD-crunching and see awful lag all the time. I usually leave my comp on without restarting (my CMOS keeps getting cleared when I power off for some reason, so I'm leaving it on even more). If I had a gig of ram I have the feeling I'd be far more satisfied.
For all you people saying there's no point cause your games don't go faster - WTF, do you expect higher quantity of RAM to make your games faster? That'll only happen if you are already too low on ram and it has to cache during gameplay. Otherwise, maybe FASTER ram would make a difference, probably a slight one again only if you were underpowered to begin with. Ram generally isn't a thing looked at to improve frames per second, but rather to multitask.
To each their own, but gimme a gig any day over this 256...
Another note... HD is critical also. If you have a shiety hd, who cares about RAM. HD first.