In the following article:

INFO: Default .AddIn file locations for Visual Studio add-ins
http://www.mztools.com/articles/2008/MZ2008001.aspx

I mentioned the problem with one of the locations (%ALLUSERSPROFILE%\Application Data\Microsoft\MSEnvShared\AddIns) that hardcodes “Application Data” subfolder, when it should be localized.

I reported the problem to Microsoft and it will be fixed in VS 2010 Beta 2:

https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=466756

All add-in developers using that location should pay attention because if Microsoft don’t follow my advice (mentioned in the bug report) of keeping the wrong location and adding a new, correct, one and they just change them instead, add-ins will be broken in international versions of Windows (because VS would no longer would search in the hardcoded path that many add-ins use). Stay tuned.