I've long since replaced the venerable Task Manager with Process Explorer from SysInternals. It's just better in every way - from the fact that it will show you which process created which other processes to the fact that the column names actually mean something. But today I found out how truly cool it is.
My machine was thrashing on something, the CPU at nearly 100%. When I fired up Process Explorer, I could see that it was the mysterious “System” process. If I'd been using Task Manager, that would have been pretty much all I could tell. But with Process Explorer, I was able to right-click, bring up properties, and see that one particular thread was the offender. Further, I was able to see the call stack for that thread. On top of that, I was able to click a button to pull up details of the device driver that was using the CPU so heavily.