On Friday Mr Blue Screen overran my machine and I had to call in the repairman. Fortunately I got a good (though expensive!) one as it took several hours to get everything sorted. It turned out the CPU fan was not speeding up when it should have been, the CPU was overheating and that most likely killed some memory and corrupted Windows.
So it was full reinstall time, after which Vista got down to downloading 30 months worth of Updates while I reinstalled programs. It took 3 days for Service Pack 1 to arrive, presumably Microsoft sensibly had security updates at the front of the queue.
The only glitch so far was overwriting my Firefox Bookmarks (duh). The latest Nvidia drivers didn't work well with my budget never state of the art card, so I reverted to the previous set. Thunderbird made no objection to my copying over all its data files in a single block.
The only problem that threw me was that my router had reacted to all this by dropping its Download speed, causing Second Life all kinds of problems. Rebooting it forced it to renegotiate speeds.