Yesterday, Apple released a new update to Lion. In an effort to not leave those who haven’t migrated to Mountain Lion behind, the OS X Lion v10.7.5 Update provides the new Gatekeeper security feature, improve Wi-Fi reliability for iMacs (models from late 2009 and newer), fixes an issue using Spotlight to search an SMB server, improve compatibility connecting to Active Directory servers (hopefully no more waiting 15 minutes to authenticate to an AD server) and also updating passwords for AD clients, resolve a video issue with some VGA projectors when connected to certain Mac notebooks, plus several other updates and fixes. You can read the entire list of fixes at http://support.apple.com/kb/HT5313?viewlocale=en_US&locale=en_US
The 10.7.5 update is recommended by Apple for all OS X Lion users.