One gig. It has two slots and can hold 2 gigs but I really don't feel a need to add more.
I also have two other user accounts that I leave open all the time. A non admin Guest account for when my friends want to use my Mac and a Testing account that I keep set to factory defaults.
My laptop is the original 17 Powerbook. The newer ones are a lot faster but I've never really felt the need to upgrade.
Here I ran Top and took a screen grab.
http://cleoslinks.com/crap/top.png