I ran into a small issue after updating XCode via the MacApp Store. Basically installing Xcode now removes the old /Developer directory from the root of your hard drive and it now lives inside of the Xcode.app directory. 

If you use the built in OS X merge tool for fixing merge issues in git repose then the following git command will break and not work. 

$> git mergetool -y

In order for it to work again you need to run the following command in terminal.

$> sudo /usr/bin/xcode-select -switch /Applications/Xcode.app/Contents/Developer

Hope this little tip helps.