I want to clear the list of projects on the start page...how do I do this? I know I can track it down in the registry, but is there an approved route to go?
I use the MRU Cleaner third party add-on to do the job. So far I haven't had any issues with it.
If you try opening up a project that can no longer be found, Visual Studio will prompt you for permission to remove it from the MRU list. So if you temporarily rename an appropriate top level folder to fake the projects' disappearance, you can get rid of the projects one by one.
I found the MRU editor from Code Project a great tool for that. No problems with it, and it works on 2003, 2005, and 2008.
There is an MSDN article here which suggests that you just move the projects to a new directory.
However, as you mentioned, the list of projects is kept in the registry under this key:
HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\<version>\ProjectMRUList
Some people have automated clearing this registry key with their own tools:
Visual Studio Most Recent Files Utility
Add-in for cleaning Visual Studio 2008 MRU Projects list