Visual Studio has multiple flags to reset various settings:
/ResetUserData - (AFAICT) Removes all user settings and makes you set them again. This will get you the initial prompt for settings again, clear your recent project history, etc.
/ResetSettings - Restores the IDE's default settings, optionally resets to the specified VSSettings file.
/ResetSkipPkgs - Clears all SkipLoading tags added to VSPackages.
/ResetAddin - Removes commands and command UI associated with the specified Add-in.
The last three show up when running devenv.exe /?. The first one seems to be undocumented/unsupported/the big hammer. From here:
Disclaimer: you will lose all your environment settings and customizations if you use this switch. It is for this reason that this switch is not officially supported and Microsoft does not advertise this switch to the public (you won't see this switch if you type devenv.exe /? in the command prompt). You should only use this switch as the last resort if you are experiencing an environment problem, and make sure you back up your environment settings by exporting them before using this switch.
On the Tools menu, click Import and Export Settings.
On the Welcome to the Import and Export Settings Wizard page, click Reset all settings and then click Next.
If you want to delete your current settings combination, choose No, just reset settings, overwriting all current settings, and then click Next. Select the programming language(s) you want to reset the setting for.
Click Finish.
The Reset Complete page alerts you to any problems encountered during the reset.
When developing extensions sometimes you just mess up, others someone else does. If you start getting errors loading even the most mundane extensions, these are the instructions to hard reset your instance.
Close Visual Studio (if you haven’t already).
Open the registry editor (regedit.exe)
Delete the HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\{version}
Delete the HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\{version}_Config
Delete the %LOCALAPPDATA%\Microsoft\VisualStudio\{version} directory.
Enjoy your brand new Visual Studio instance.
Use {version}=10.0 for Visual Studio 2010
Use {version}=11.0 for Visual Studio 2012
Use {version}=12.0 for Visual Studio 2013
If on the other side you want to reset the experimental hive you can do the same to with the ‘{version}Exp’ ones.
Click on Tools menu > Import and Export Settings > Reset all settings > Next > "No, just reset settings, overwriting all current settings" > Next > Finish.