I have noticed that my computer can hold a LOT more programs and not lag a single bit.
****, I had counterstrike loaded, ms picture it, about 37 music videos downloading, on and on, and in CS I didn't lag a single bit. Overall, I opened every program I could with my computer, even had spyware and virus scans running to bog it down. But I still didn't lag a single bit, granted I was only able to suck up 1.3 gig worth of the memory, so I still had roughly 700 megs free.
I figured that my computer was just "that" fast before, that adding more ram didn't make it noticably faster... I have noticed though, that I can load more programs and not worry about it bogging down. Then again, it didn't bog down much when I had 1gb of ram, but regardless I have noticed that.