I tried a commercial uninstaller called advanced uninstaller pro for 30 days and i found it made a dramatic difference to my PC as it removed alot of stuff that had been left behinf when uninstalling and it cleaned up the registry as well. Using defrag also helps but i found that you have to run it a few times consecutively to defrag the hard drive properly: even after it finishes and tells you drive is defragemented you can run it again and it will continue to defrag, upto a POINT.
