640MB presently..... though I'm thinking it's about time I pop in some more.
Running anything very memory intensive in the background while playing Morrowind steals all my RAM in an instant.

Been starting to multi-task a bit more heavily then I did in the past, and when I have FTP proggy, FrontPage, and PhotoShop running simultaneously it gets pretty close to hitting the pagefile with regularity, and if I saw need to run Adobe 5, or my Scanning proggy, or even Corel at the same time I'll easily surpass the DRAM I have available.
Probably jump up to 768MB maybe a little more. I can't see myself needing 1GB as even my most intensive usage generally only sits around 800MB memory usage.