Normally, hibernating Vista overnight is fine.
But something seems to have caused it to get right confused last night.
First, it took a couple of minutes for anything to be visible, and then things were veeeeery slow, if they were responding at all. Opera didn't respond, Task Manager did. Alt+Tab took a minute or so for the bar of programs to appear. The Sidebar had one applet show the correct time, but the clock and the calendar were still on yesterday. The clock at the bottom right wasn't updating at all, even 40(!!) minutes later.
The Task Manager showed that The Sims 2 was slowly getting more memory, which is strange since it usually occupies very little when it's minimised (most of it gets swapped out and doesn't get swapped in until I switch to it).
I thought of cache thrash, but then I would have expected more hard disk grinding noise.
It seemed as if it was just really confused internally about what was up and who was going to get memory or CPU time or something.
I found it extremely stressful and annoying.
In the end, I just power-cycled the machine.