I use 4g as my sig shows. I do a bit of photo editing so will upgrade to 8gb when I can be bothered/con the wife.
Anything over this and I think it is mainly video and sound editors that will see the benifit.
For every day to day use of computers and the resources required for the normal person 4gb should be fine.
As to ddr3 over ddr2, is the speed
increase worth the money?