Apple posted a list of software titles it considers incompatible with Mac OS X 10.6 on its Web site, and noted that certain apps will be blocked from launching once Snow Leopard is installed, too.
The Knowledge Base article breaks incompatible applications into two categories: Restricted during installation and migration, and Restricted from opening.
Applications that are restricted during installation are moved to an Incompatible Software directory at the root level of your hard drive. The list of applications includes, in part, Parallels Desktop 2.5 and earlier, VirusScan 8.6, Norton AntiVirus 11, and launch2net.
Apps that fall in the restricted from opening group include Parallels Desktop 3.0, VirusBarrier X4 10.14.4 and earlier, EyeTV 3.0 and 3.1, Aperture 2.1.1 and earlier, Keynote 2.0.2 and earlier, and more.
Apple is advising Snow Leopard users to check with developers to see if newer application versions are available, which is good advice because in many cases Mac OS X 10.6-compatible updates are ready for download.