Typical example is when shutting down a memoryintensive application. It can take quite a while before the computer gets back up to speed. Is there some inherent cost in releasing memory? Or is it throttled by some kind of harddrive activity, and if so is there any good way to track that?

I usually bring up task manager when a computer is running slow, and usually sorting by cpu activity can show what process is causing the problem, but sometimes there is no activity showing. And yes I "show processes from all users", I have been wondering this since the days win2k :)