Yeah, I currently have only 1GB but planning on upping to 2 when I upgrade to Vista. You have to also consider 3D gaming too, if you play any on your PC. With that said I may go up to 2.5, I don't know.
Just a heads up I found Corsair PRO LED 800 mhz PC 6400 modules at Fry's .com for 239.99 for the 2 gig kits (5-5-5-12). They say special order, so I think it might take a little longer to get them but it's a great deal. http://shop4.outpost.com/product/4776319;jsessionid=LQfJFYqDCPQ4oCzlYelHuA