I just lost 3 hours of support time due to Windows Update. I switched off my computer at lunchtime and XP said it would install another update from Windows. I left the computer to update itself as I've never had problems before.
When I came back this evening, I couldn't connect to the BT wireless router. My other PC with an Ethernet cable was fine but my main PC refused to connect. I used my wife's PC in the end and found that a lot of other people were experiencing the same thing. The fix turned out to require cranking down the AVG firwall setting. Very frustrating!