I went from 128 to 192 and its been a major boost. Quake3 is much smoother, and there are less pauses. (When I hit tab, to see the score board, my system would pause for 5-6 seconds while there was some major harddrive swapping. Im guessing it was loading player models or their logos or something along those lines). Now it doesnt do it.
I can play Half-Life TFC for hours, and it will only hit my harddrive every 10 minutes or so.. Pretty much all of the game can fit into the RAM.