Of course version 5.1.1 also includes the a number of fixes and overall stability improvements.
Safari 5.1.1 also contains various fixes and improvements to performance, stability, usability, compatibility, accessibility and security, including fixes that:
Address issues that could cause hangs and excessive memory usage
Improve stability when using Find, dragging tabs, and managing extensions
Improve stability for netflix.com and other websites that use the Silverlight plug-in
Add a Show Downloads item to the View menu
Improve the consistency of the pinch to zoom gesture
Address issues in full screen that affected search suggestions, URL updating, window sizing, and the title bar
Address an issue that could prevent East Asian character input into webpages with Flash content
Address an issue that could cause Safari to open links in windows instead of tabs
Improve PDF handling
Address an issue that could affect cookie and data deletion
Address an issue that could cause History items to appear incorrectly
Correct the text in application download alerts
Improve compatibility with webpages with Flash video embedded from vimeo.com and other websites
Improve printing from Safari
Address an issue that could prevent the Google Safe Browsing Service from updating
For detailed information about the security content of this update, please visit this site: http://support.apple.com/kb/HT1222.
For more detail about Safari, visit apple.com/safari.
UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:7.0.1) Gecko/20100101 Firefox/7.0.1