A few days ago, I encountered a problem with Visual Studio.
Every time I tried to open an xaml file in a WP7 project Visual Studio would crash without showing any error. The Event Log would also not show anything about VS crashing.
I knew this project worked the last time I worked on it a few weeks ago, so something must have changed since then.
It turns out that I had installed the Silverlight 5 Developer Runtime after I opened the project last time.
I tried uninstalling the Silverlight 5 Tools, but it had no effect. Turns out that when installing the Silverlight 5 Developer Runtime, it messes with some of the Silverlight 4 runtime, making projects based on SL4 (like WP7) crash on rendering.
When I uninstalled Silverlight 5 and installed the old Silverlight 4 Runtime, everything worked normal again.
So word of advice: If you develop for WP7, don't install Silverlight 5.