Some users have reported an issue in which Safari 5.0 renders some web pages with blurry fonts. Apple Discussion poster Peter Whysall writes:
“Since installing Safari 5, I am seeing certain websites where the body text appears to have broken sub-pixel antialiasing. To confuse matters further, this problem can show in text on one part of a page, but not in others.
Peter also posted a screenshot of the problem (Safari on the left — click image to enlarge).
As noted by several users, this problem can be solved by disabling Flash. This can be easily accomplished with ClickToFlash, This handy utility allows users to–as the name implies–trigger playback of Flash content on web pages via a mouse click. It also swaps out Flash-based YouTube videos for higher-quality H.264 versions (something that can also be accomplished by joining the YouTube HTML5 beta).
Failing ClickToFlash, you can download the Flash uninstaller to remove Flash altogether.