I have just heard back from SONY, where they have been able to repro my particular "hang". If you too are using an external Monitor, through firewire, this will be great news for you too as there IS a temporary workaround . This is what they say:
"We were recently able to repro this hang, and figured out the root cause, and will have a fix in the next Vegas Pro 9 update.
SONY Madison is definitely on the case.
Cheers
Grazie