In a burst of inspiration, I ran the debugger on the debugger and hit break. It turns out that the copy of Codewright for .NET that I installed into Visual Studio is trying to find out what's on the clipboard. But since the clipboard is a steaming pile of entrails (see tonight's CSI for more), it fails. Over and over again. Although it certainly doesn't use much CPU while doing so...
Tomorrow, I find a machine without Codewright and try again.