Apple has released this support document outlining what applications are known to be incompatible with Snow Leopard, and which applications simply won’t launch in Snow Leopard.
Software restricted during installation and migration
During installation, Snow Leopard moves known-incompatible software to a folder named Incompatible Software at the root level of the hard drive. If you see this folder on your Mac, use the table below to check with the software vendor to see if any Mac OS X v10.6 Snow Leopard-compatible updates are available.
Some of the know incompatible software titles include. Parallels v 2.5 and earlier, Norton Antivirus v11.0, and At&T Laptop Connect Card v 1.0.4,1.0.5,1.10.0, just to name the large developers. Most of the applications that are incompatible with Snow Leopard seem to be from relatively unheard of software developers.
Software restricted from opening
After installation if you try to open (“launch”) software known to quit unexpectedly, Snow Leopard will prevent the application from opening and you will receive a dialog notifying you of the incompatibility. If you see such a dialog on your Mac, use the table below, then check with the software vendor to see if any Mac OS X v10.6 Snow Leopard-compatible updates are available.
Some of the big name applications that will not launch in Snow Leopard include: Parallels Desktop v3.0, Ratatouille v1.1, Aperture v2.1.1 and earlier, and Keynote 4.2.5. This apps will not even launch in Snow Leopard, so don’t bother. Personally I’m kinda surprised these apps don’t run, especially some of the Apple apps.