On the heels of the 10.5.8 update, Apple has added Safari 4.0.3 to that list, citing the following:
This update is recommended for all Safari users and includes improvements to stability, compatibility and security including:
- Stability improvements for webpages that use the HTML 5 video tag
- Fixes an issue that prevented some users from logging into iWork.com
- Fixes an issue that could cause web content to be displayed in greyscale instead of color
In depth (as in depth as Apple gets...) information can be found on Apple's website.
Run Software Update to download the latest version.