Mouse Button 3 will no longer activate spaces in Snow Leopard.
Any ideas on how to get this working again?
My answer about Exposé not working from here:
I am using the Logitech Control Center, but I also found that setting buttons to Spaces or Expose didn't work. Instead, I assigned the buttons to the function key which called those commands and it has been working find since.
The solution that was accepted was to delete the ~/Library/Preferences/com.apple.symbolichotkeys.plist file.
Go to System preferences -> Mouse-> Enable your secondary mouse button key to spaces and you are wellset to go. (You should have enabled spaces also in spaces setting in system prefenrences.)