"Dan Gruber(that is, Daring Fireball)":http://www.daringfireball.net/ has written an excellent "article on anti-aliasing in Max OS X Web Browsers":http://www.daringfireball.net/2003/03/antiantialiasing.html. It's a two-part series, of which this is the second. The "first article":http://daringfireball.net/2003/03/antialiasing.html defines the basis of the problem.
Safari.
"Safari":http://www.apple.com/safari/ renders some fonts *wrong*. You *should not* render monospace fonts anti-aliased.
(via "Hivelogic(Dan Benjamin)":http://www.hivelogic.com/299.html )