Just a quick post.. recently my desktop and laptop Macs have become so irritating to use - every time I tried to do anything it seemed like it would freeze and give me the spinning beach ball of doom for ages. Really computer-smashingly annoying.
BUT! The fixes I found on this web page... www.whyismymacsoslow.net have really worked and fixed them both back to useable computer status. I ignored the preferences fix but did the repair permissions and delete cache fixes. Worked like a charm!