A number of important issues have been addressed. 5.1.2 is a highly recommended upgrade. Highlights include:

• LDAP Synchronization and Authentication
• JSR 286 Conformance
• Transaction (Spring Tx) Propogation was not functioning properly
• Layout Caching handling of Internationalized Websites
• Removed a situation where database connections may leak under heavy load
• Improvements to Spring Integration and Transactions
• Siteminder Integration (via Authentication Pipeline). Thanks Mika!
• ...and hundreds of additional Selenium Tests

Complete releases notes can be found at http://support.liferay.com/secure/ReleaseNote.jspa?version=10321&styleName=Html&projectId=10014&Create=Create

Downloads:

http://www.liferay.com/web/guest/downloads/portal

Plugins (Themes, Portlets, etc)

http://www.liferay.com/web/guest/downloads/official_plugins

http://www.liferay.com/web/guest/downloads/community_plugins

5.2.0 is about a month away. Lots of goodies in there including a new control / admin panel, knowledge base application, new tagging system for both taxonomies and folksonomies, private messaging, and much much more.