Ugh. So I just stumbled onto a bug in Visual Studio. Those of you who have upgraded to VS 2008 SP1, use floating toolbar windows, (probably on a second monitor) and debug your code have no doubt come across this. When you combine all three of these circumstances, pressing F5 to debug your code causes VS to crash with an irrecoverable internal error.
You can actually tell that it's a C++ error since you don't get any JIT or unhanded exception error messages. Nope. Just an unmanaged, swift death for Visual Studio. At least you won't lose any work; this only happens after a successful compilation as Visual Studio "turns over" and switches to its debug configuration (when all your debug-time windows and toolbars replace your design-time ones).
So when I put the pieces together, I said to myself: "Wait, it crashes when I drag toolbars onto my second monitor? No that can't be it..." And then I spent like two more days coding tentatively, trying not to piss off Visual Studio while deterministically reproducing this error.
Well now we know the issue. I've submitted a bug to Microsoft. Please track it here.
The only workaround is to simply change your life around so as to not enter debug mode with floating toolbar windows. Hopefully, a hotfix will come out soon!