With the introduction of Mac OS X Snow Leopard, Apple has decided to disable graphical configuration of font smoothing. Fortunately, there is a workaround!
Previously on Leopard
In Leopard and earlier versions of Mac OS X, if you opened System Preferences and chose Appearance, you could choose the level of font smoothing on your monitor with a handy drop down box.
On Snow Leopard…
For some reason, Apple decided in Snow Leopard to to disable graphical configuration of font smoothing aside from a single checkbox, instead relying on LCDs to report what settings should be used. The problem is, support for this is spotty and sometimes the results look terrible.
Fortunately you can still adjust this manually. Open the Terminal in your Utilities folder, then enter the following code on one line. Replace the "2" with a number between 1 and 4, depending on how much smoothing you want.
defaults -currentHost write -globalDomain AppleFontSmoothing -int 2
The changes will only take effect on newly opened applications. The easiest way I've found is just to log out and log in again.
Heaven knows why Apple user interface designers decided to remove access to this feature.