I've got two T41's and two T42's that my kids use. Admittedly, these are old bits of kit now, but all worked fine when I used XP and even when I first installed Windows 7. However, I've just installed the thinkvantage system update, set each machine to install the latest fixes and I have also set all four machines to install the latest windows updates.
All four machines updated automatically and have now all stopped shutting down. They logoff and stop everything, but then get stuck on the windows shutdown screen. The hard drive light flashes for a while and then goes out, just leaving the power and wireless lights on and I have to shut them down by holding the power button.
They all work fine apart from this, but I have a suspicion that they randomly shutdown and restart because I've left them overnight to see if they ever complete a shutdown and a few hours later I find they have restarted.
I only run win 7, office and AVG as I haven't got round to installing anything else yet because of this issue.