Now, to be clear, I believe that I am still working in classic mode and running VS 2008 as Administrator to get around all the issues that came up when Vista came out, so this may not apply to you.
But, after installing SP1 for Vista, I could no longer debug my web applications running on IIS7. I worried about some major problem that would take hours if not days to fix.
As it turns out, the WAS service was not set to auto-start, which prevented any of the application pools from starting, which prevented the WWW service from starting.
Started WAS (and set to auto-start), checked in IIS7 manager to make sure the pools were started, and everything was good.