I recompiled our add in to work with Visual Studio 2008.  For anyone that's interested, here's the gotchas I encountered:

1. The FogBugzVisualStudio.AddIn file has a <version> tag in it which needs to be changed to 9.0 for 2008.
2. During installation of your addin, you probably wrote your addin's directory to the registry key
   HKLM\SOFTWARE\Microsoft\VisualStudio\8.0\AutomationOptions\LookInFolders
   The 8.0 in this key should also change to 9.0.
3. If you want to install your same add-in so it works for VS2005 AND VS2008, you'll have to install it to two different directories.  One with the .AddIn file that says 8.0 (for VS2005) and the appropriate registry key pointing to that directory, and the other that says 9.0 (and the 9.0 reg key pointing to that directory).
4. VS2008 now does some funky things with regards to the tab picture.  The transparency color has changed, which is discussed in this article.  Also, you used to be able to pass a BITMAP handle to SetTabPicture, but now it takes an IPicture, so you'll have to call out to OleCreatePictureIndirect to translate your HBITMAP to an IPictureDisp.

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