Rated 4 out of 5 stars
It certainly makes fonts look nicer, but it also seems to break fonts in certain areas of Firefox 4. Namely in the Download Manager when scrolling through a long list. That doesn't make the addon unusable for sure, but it's something that needs to be fixed.3 stars until the font issues this causes are fixed.
Edit: Version 11.03.25.01 seems to fix some of the problems.