
For some reason, Apple decided in Snow Leopard to disable graphical configuration of font smoothing (aka sub pixel rendering) and instead rely upon LCDs to report what settings should be used. Problem is, support for this is spotty with some panels and the resulting fonts look rough and pixelated.
On regular Leopard if you open the Appearance prefpane you’re presented with a drop down box where you can choose how heavy font smoothing is applied, as shown in the screenshot above. On Snow Leopard all you get is an ambiguous checkbox saying "Use LCD font smoothing when available" without any option to choose by how much:

Fortunately you can still adjust this manually by opening Terminal.app and entering the following command with an integer between 1 and 4 (representing the 4 previously available options), then re-opening your applications. Easiest way is to enter this, then log out and log back in.
defaults -currentHost write -globalDomain AppleFontSmoothing -int 2
Heaven knows why Apple user interface designers decided to remove access to this feature.