One of the Macs in our office has just been updated to Snow Leopard (yeah, we're a bit behind the rest of the world) and we found that Motion 4 and Compressor 3.5, the versions in Final Cut Studio 2, were crashing. Compressor would hang or crash if you tried to change the output location from the default 'Source', and Motion was particularly frustrating because you couldn't even save a project, or export from an unsaved project, without it crashing and losing all your work.
After a bit of searching I eventually found a fix. It was tricky to find because it's not an issue specific to Motion or Compressor, but across all of Apple's Pro applications after Mac OS has been updated to 10.6 Snow Leopard. The fix is here:
It requires a bit of typing in Terminal which can be a bit scary due to using the superuser commands. Copy and paste the lines in the instructions if you're not a confident typist!