There seem to be an issue with Fusion 5.0.3 (lastest) with Moutain Lino OS X. First it won't ungrab from the guest VM if I move the mouse cursor outside of the guest VM. I have uninstalled and reinstalled VM Tools to no avail. The only way to get out of the guest VM is by pression Ctrl-Command. It did not used to do this until I upgraded to Mountain Lion. I tested this on Windows 7 64-bit guest VM & XP and it's the same problem. Further, sometimes the mouse left click just stop working in the guest OS. I would have to restart the guest VM.
Anyone having this problem?