The changes are listed here with the most significant being that it’s required to install Lion via the Mac App Store :
The 10.6.8 update is recommended for all users running Mac OS X Snow Leopard and includes general operating system fixes that enhance the stability, compatibility, and security of your Mac, including fixes that:
- Enhance the Mac App Store to get your Mac ready to upgrade to Mac OS X Lion
- Resolve an issue that may cause Preview to unexpectedly quit
- Improve support for IPv6
- Improve VPN reliability
- Identify and remove known variants of Mac Defender
For detailed information on this update, please visit this website:http://support.apple.com/kb/HT4561.
For information on the security content of this update, please visit:http://support.apple.com/kb/HT1222.
The update weighs in at 237.5MB and the build number is 10K540. A direct download is available here from Apple.