I am running Windows Vista 64-bit, I think I was on the latest service pack.
I tried to restart the computer today, and it has been at the "Please do not power off or unplug your machine. Installing update 1 of 1 .." for several hours now. The spinner is still spinning, the dots are still moving. (I didn't look ahead of time to see what update(s) it had waiting, so I'm not sure what it is trying to apply.)
Do I let this run indefinitely? Is there a point at which I ought to give up and hard-boot it? If I did, could that cause me some serious problems?