Apple Releases OS X 10.6.8 Software Update; Next Stop: Lion
According to changelog, this update is intended to fix a number of general OS issues that will enhance stability, compatibility and security. It's also the last major step before Lion; Apple even says that it updates the Mac App Store "to upgrade to OS X Lion." The update also fixes an issue that could cause Preview to quit without cause, and it also improves support for IPv6, VPN connections and the ability to remove other versions of Mac Defender.
It's available right now in your Software Update; let us know if you run into any glitches in comments!