So last night I installed Visual Studio 2008 RTM on my laptop. This was a clean install - I did not have any beta versions of VS2008 installed. When I went to try and do anything in VS2008, I kept getting the message 'Visual Studio has encountered an unexpected error.". This error happens when I try to do anything, including VS2008. The only way to close VS2008 was using Task Manager. Most annoying.
A quick search, and I see that JP Boodhoo has the same problem. The comments on JP's blog seems to point to VisualSVN as being the culprit. I uninstalled VisualSVN, and everything seems to be working again. So, the problem was the add-in. I then installed a new version of VisualSVN (v1.3.1), and VS2008 seems to be working again.