Apple released Snow Leopard, Mac OS X 10.6, to a eagerly anticipating base of loyal fans. The problem is even though the OS is ready for prime-time, some of your applications may not be ready for it.
It's an issue that faces most OS upgrade cycles: the OS updates and then some of your currently installed apps need to be patched to work How do you know which mission critical app of your will stop working properly once you upgrade?
The nice people contributing to Wikidot have a page with an extensive list of apps and their compatibility with Snow Leopard. As a wiki you are encouraged to fill in the blanks. The site can be viewed here: http://snowleopard.wikidot.com/