I've turned on subpixel font rendering on my work computer running Linux. Apparently it doesn't autodetect my LCD properly, because I think it's supposed to be on by default if you have an LCD, but I do and it isn't for me.
What's subpixel font rendering, you ask? Well, LCDs use three vertical "stripes", each a third of a pixel wide, of red, green, and blue, to render a single colored pixel. Since these stripes are laid out in a predictable order, you can effectively render with triple the horizontal resolution by addressing the individual color stripes. Read more at Gibson's page.
Anyway, if you want to find out whether you're using subpixel rendering, fire up 'xmag' and click on some text. Your text is probably anti-aliased, but is it colorful?