I wanna know. What amount of RAM works for you and what do you do on your Mac Pro system. I'll start: I have 5GB. I upgrade from 3GB which I upgraded from 2x512MB (1GB Factory RAM). 3GB was working okay for a while until I really got into using Aperture and Photoshop a lot. I started to notice a lot of disk activity and my system became sluggish and I was embarrassed to show people my powerful Mac Pro when it was acting like that. I upgraded from 3GB recently to 5GB from OWC (otherworldcomputing.com) and I can't be happier. My machine is always running fast now and even when I'm working on huge HDR panoramas. Since I've had 5GB of RAM, I get only about 100 pageouts per day. Before the 2 extra gigs, I was getting thousands pageouts and really crappy performance until I restarted.