It is possible that some users may experience an issue with their Bluetooth mouse not being able to wake their Mac from Sleep Mode after upgrading to Mac OS X 10.6.x Snow Leopard. Apple Support Discussions user "Cyd" opened a thread for just that problem. "Cyd" reports:
My Apple bluetooth wireless mouse loses it's connection when my computer goes to sleep. Before SL I could wake my computer with my mouse. Now I can't because the mouse doesn't have a connection. It seems that sleep turns off bluetooth connectivity.
The setting to check when experiencing this issue is located in:
System Preferences > Bluetooth > Advanced...
Be sure to check the box to "Allow Bluetooth devices to wake this computer." It appears as though installing Snow Leopard may reset this setting for some users. If the issue continues to arise, or you are experiencing similar Bluetooth problems, try deleting the "com.apple.Bluetooth.plist" file located here:
MacintoshHD > Library > PreferencesAs always, be sure to have a stable and current backup of your system before troubleshooting at the root level of your Mac. You should test your Bluetooth before emptying your trash to preserve your preference file if needed. There is even more discussion on Bluetooth issues in Snow Leopard here. How is Bluetooth working for you? Let us know in the comments!