COM Shim Wizard for IDTExtensibility (Shared Addins) Now Available for Visual Studio 2005
I've blogged before about the need for shimming non-VSTO shared managed add-ins. Misha Shneerson and Andrew Whitechapel created a COM Shim Wizard that worked with Visual Studio 2003. They've now updated the wizard and it is available on MSDN.
You should use this shim wizard if you are building shared IDTExtensibility2 based add-ins for Office. A shim gives you appdomain isolation and some other goodness.
If you are developing add-ins for Outlook 2003, VSTO 2005 provides a better add-in project that you should use instead of Shared Add-ins.
If you are developing add-ins for Office 2007, the VSTO v3 CTP has add-in support for all the Office applications and so you won't need this COM Shim Wizard: http://msdn.microsoft.com/vstudio/future