I had Xcode 4.1 preview 5 working fine but decided to upgrade to the final xcode 4.1 thru the App store. I uninstalled Xcode first...
sudo /Developer/Library/u
Just bought a Mac, what I had to do to make it work after installing Xcode and seeing that /usr/bin doesn't have gcc, was: Enter Xcode preferences going over to the downloads tab and install Command Line Tools. After setting up my developer account and downloading the tools I opened terminal and typed
rvm install 1.9.3 --with-gcc=clang
and everything compiled and works.