The Add-In Manager of Visual Studio 2005 got broken...and won't be fixed for SP1
My MZ-Tools 2005 add-in, like many others migrated from VS.NET 2002/2003 still uses COM registration, rather than XML registration (.AddIn file) and since it wants to be a good citizen in the new Windows Vista operating system, it uses HKEY_LOCAL_MACHINE to register within Visual Studio 2005 so the administrator installing it makes it available to other users of the machine (which may be other than the administrator). Previously I was using HKEY_CURRENT_USER but since I changed to HKEY_LOCAL_MACHINE, I am experiencing a problem that many of you will have seen: the Add-in Manager of VS 2005 does not persist changes in the Startup column if the add-in uses COM registration, even if you are an administrator of the machine.
I investigated this issue in the Microsoft Connect database and to my consternation it was reported twice but either the bug reports were not very clear or the Microsoft team failed to understand the problem so it is still unsolved, I reported it a third time, very clearly (I hope) but MS has answered that there is no time to fix it for SP1. So, if your add-in is affected by this problem take a look and vote for the bug to get it fixed for SP2 or VS "Orcas":
http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=238492