The 10.6.3 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:

improve the reliability and compatibility of QuickTime X
address compatibility issues with OpenGL-based applications
address an issue that causes background message colors to display incorrectly in Mail
resolve an issue that prevented files with the # or & characters in their names from opening in Rosetta applications
resolve an issue that prevented files from copying to Windows file servers
improve performance of Logic Pro 9 and Main Stage 2 when running in 64-bit mode
improve sleep and wake reliability when using Bonjour wake on demand
address a color issue in iMovie with HD content
improve printing reliability
resolve issues with recurring events in iCal when connected to an Exchange server
improve the reliability of 3rd party USB input devices
fix glowing, stuck, or dark pixels when viewing video from the iMac (Late 2009) built-in iSight camera

System Requirements
Mac OS X 10.6.2