i routinely see over 1GB of usage in my rig in sig. with it i game coh and bf2, use the entire adobe suite and then the normal stuff.
my laptop - ibm t42, p-m @ 1.4, xp pro, 512MB rarely if ever goes over the 512MB that is in there. its uses are internet, word, email - very basic stuff.
my server machine - xp2000, win2kpro, 512MB which runs a couple websites that are db driven by mysql and some static ones, running apache, php, mysql and is also the depository for the hdd images from the other machines routinely goes over its 512MB but i have just been too lazy to add another 512MB stick in it. that machine is one 24/7 and only gets a reboot when the windows update needs it. it probably won't get a ram upgrade until i switch its primary (os/apps/dbs) and secondary (sites) hdds over to 10K scsi, which may be some time. still solid and reliable as a rock, but doe get a bit sluggish especially when it is backing up data, running a log analyzer for the sites and also getting a image all at the same time. in fact i am probably maxing the cpu way to much, so i guess when i switch to a new rig for me, my rig in sig will be the next home server rig...