Well, given that he's already got a gig - I will be really surprised if he sees any significant benefit to CS2 by adding more.
I suppose that depends on what he's doing. My C2D MBP has 2GB in it and I can run short with a lot of what I do in Photoshop pretty easily. Then again, I occasionally find myself needing Maya or Lightwave open along with Photoshop and well, 2GB just doesn't cut it...
gonnabuyamac, next couple times CS2 is sluggish for you, try launching Activity Monitor to see how much free memory you've got and how much memory your various apps are using. Note that "inactive memory" will not be reported as free, but should be available to other apps as needed.
His activity monitor reports seem a little off... Then again, I'm not sure what I'm getting with mine, haven't really studied it and I don't have the notebook handy right now.