Safari 5.1.4 for OS X Lion includes changes that:

Improve JavaScript performance up to 11% over Safari 5.1.3*
Improve responsiveness when typing into the search field after changing network configurations, or with an intermittent network connection
Address an issue that could cause webpages to flash white when switching between Safari windows
Address issues that prevented printing U.S. Postal Service shipping labels and embedded PDFs
Preserve links in PDFs saved from webpages
Fix an issue that could make Flash content appear incomplete after using gesture zooming
Fix an issue that could cause the screen to dim while watching HTML5 video
Improve stability, compatibility, and startup time when using extensions
Allow cookies set during regular browsing to be available after using Private Browsing
Fix an issue that could cause some data to be left behind after pressing the “Remove All Website Data” button
For detailed information about the security content of this update, please visit: support.apple.com/kb/HT1222

* Testing conducted by Apple in January 2012 on a 2.7 GHz Quad-Core Intel Core i5-based iMac 21.5-inch system using OS X Lion v10.7.3 and configured with 4 GB of RAM and an AMD Radeon HD 6770M with 512 MB of VRAM. JavaScript benchmark based on SunSpider 0.9.1. Performance will vary based on system configuration, network connection, and other factors.