The 'delights' of...
On Monday some server somewhere decided that I should be upgraded on my work laptop to Vista Service Pack 2. I installed it went through the reboot it requested and everything seemed ok, I then went back to using my Linux (Ubuntu) installation until the afternoon of the next day when I needed to do some work on Vista.
I was out of luck - I got a dialog suggesting this was the first time I'd logged in. Few of the options in the 'Start' menu worked, couldn't get to the control panel, it claimed I needed to reboot to reenable UAC (which I had never disabled). I rebooted and still the strange setup continued. I had another go today when I thought about rolling back to before the upgrade - but as you see from the screenshot the system is uncertain as to whether I have a C drive(!) and how many of them there are - I do (just one) and neither of them appear to have a saved state. I was working from home, so I decided I needed another pair of eyes and headed into the office whereupon all the problems went away! Googled a lot and it looks as if there's some sort of issue with SP2 and removable hardware - at home I don't connect a keyboard or an external monitor. I tried rebooting without these didn't see the problem and decided that it must have sorted itself out.
Unfortunately at home this evening the problem is back. I'll post here when I find the solution - at the moment all I can guess is some problem with roving profiles one of which is extremely broken but why it thinks I've roving I don't know.