Update: The plist trick doesn't work with XCode 4 -_- Sorry! If you want to have VIM-like XCode you should have a look at XVim.
You probably know that OS X has emacs-like keybindings by default, for some things like ctrl+a to go to the beginning of the line and ctrl+e for the opposite.
However, you can actually customise this to your liking by simply editing
I read about this on the High Order Blog and there are also more detailed instructions and very nice posts about Xcode, Vim etc.
Gosh this is so awesome :-D