Thanks for the response -
I only know one way to do updates - that's through 'App Store' - that's the way I did it - are you suggesting another way?
It's a factory fitted Solid State Drive in my machine... I checked the "SMART" status in Disk Utility, and had already run a Disk Check & Permissions repair after the first lockup as I had to force a poweroff (all checked out fine.)
Version 5.0.1 had been working fine all morning, so I uninstalled 5.0.1 and re-installed 5.0.2 at lunch time ... it's been fine for 7.5 hours so far (so looking good.)
I'll run a disk check in the Windows 7 VM as well, just in case this indicates anything.
I'll see if it holds out through to tomorrow morning when I wake the mac from sleep, and then take the small step up to 5.0.3.