System Memory: sweet spots, plateaus, recommended amounts

[TBerk]

I'm running 9.04 on a 3G dual core P4. I was wondering what the amount of RAM 'plateaus are with linux;

what would be the bare min using a graphical interface, what range is considered the 'sweet spot' (as in between xxx and yyy you will work great but won't see much difference in the range...) and what plateaus exist in the realm of "after zzz amount of RAM your improvement begins to take off...".

[logos34]

https://help.ubuntu.com/community/In...emRequirements

gnome desktop runs great on 512 mb