It will be a waste on a 32bit OS, and unless you are having problems running your 64bit linux, then dont bother. I run 4gb, and the only OS Im glad I have it for is Vista.
I could never see a difference in XP (outside of Crysis), and I DEFINITELY havent seen a difference in Kubuntu.
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Who do you carry that torch for, my young man?
Do you believe in anything?
Do you carry it around just to burn things down?