[ubuntu] Memory management: how can I make Ubuntu run like new again?

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http://ubuntuforums.org – My computer is running slowly. I think it is wasting memory. I'm running 11.04 on a 7 year old Dell Latitude D610 laptop. When I first installed Ubuntu, it breathed new life into a computer that had slowed to the limits of usability. It slowed down over time, but it returned to its best performance when I formatted it again while I was upgrading to 11.04. Its gotten pretty slow once more. I suspect I could restore it again the way I did before, but is there a way to remove all the crap slowing down my computer without wiping the whole thing clean? (Hardware)