I have upgraded to 10.8.3 and then Fusion 5.0.3 ..
I no longer have the crashing issues related to OSX video drivers.
I now seem to have a new problem - the whole system freezes when switching between VM's - the mouse locks, the MacBook Pro Retina gets really hot and the fans come on full.
I left it for about 5 minutes and it did not come back, so I had to switch off the machine 
I've only had 5.0.3 for 2 days, and this has happened three times now during my normal daily usage (I run a Windows 7 VM, Windows XP VM, and Debian VM)
I have not changed my way of working, this was all working OK under 5.0.1 up until the latest update.
This is my work laptop, I dont know what to do, I'm so deflated.
Is anyone else having this, or am I an isolated case?
(I'll get back to support to find out how to troubleshoot this.)