**Update for latest version**
Visual Studio 2015:
%USERPROFILE%\Documents\Visual Studio 2015
Visual Studio 2017:
%USERPROFILE%\Documents\Visual Studio 2017
Also have a look at these folders:
%USERPROFILE%\AppData\Local\Microsoft\VisualStudio\...
%USERPROFILE%\AppData\Roaming\Microsoft\VisualStudio\...