TaskInfo is totally worth the shareware fee for any power user of Windows. It provides vast information about processes and the system, is completely stable (I’ve been using it on three systems for 3 or 4 years with no problems), and doesn’t seem to be too hard on system resources itself.
I just used it to check progress on a download. I visited a page that embeds a QuickTime plugin, which was not providing any indication of the download progress. However, I could pop up TaskInfo and see the files Firefox was accessing, and where in the file the file pointer was. It was easy enough to see which file was being used to cache the download, and how many bytes had been written so far.