I believe this to be a bug and would not recommend anyone repeats what i have detailed below as it killed my install:
For some reason my AVwizard was appearing on each boot. This was not a huge problem, i could just click through everything and then MCE would start fine.
Today, I accidentally (bit hung over) selected the wrong resolution but didnt notice until the confirmation screen at the end of the avwizard. I used the right button on my mouse to go back to the beginning of the AVwizard expecting to be able to select the correct resolution and all would be well. What actually happened was the AVwizard became VERY slow to respond at the resolution select screen. I selected 720p (which i have been using for a few months with no problem), at the preview resolution stage the top 3rd of my screen had mutlicolour lines and the machine froze. I restarted and during the MCE start up received all sorts of error messages, hard drive full, incorrect use for the MCE services, samba unavailable etc.
I am reinstalling now.
The point to take away i think is that somehow returning to the very beginning of the AVwizard from the confirmation screen has caused something to die in my install (sorry cant be more specific). I am running the latest Alpha release of 0810 with nvidia 185.14 drivers and alsa 1.0.20.
(If nothing else then i hope this saves someone else my pain!).