Apple has released an update for Snow Leopard today which fixes many issues with the Operating System. Update v10.6.3 as it's known fixes various security, compatibility and stability issues with the OS and includes amongst many others the following updates and 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

To update Snow Leopard to the latest version simply go to Software Update in the Apple menu. Your system will then be scanned for any updates that are required. Any updates that exist will then be listed in the update program. Depending on what's required the update download size will vary from machine to machine.

Some updates are required before others can be applied to Apple recommend that Software Update is run several times to ensure that all the updates have been applied.

You can also download and apply the update manually using the update installer. This is quite a hefty download at just over 700MB but at least the update can be applied to multiple machines without having to download it all the time.

For more details see the official About the Mac OS X v10.6.3 Update page.