The clean separation between command-keys (for app-behavior) and control-keys (for emacs-like text navigation) is far and away my favorite aspect of using MacOS. I know it sounds crazy, but I navigate through text far more frequently than anything else. The ability to further customize[1] these to support meta-keys (using option) and rebinding caps-lock to control makes for a very powerful experience.

1. http://www.hcs.harvard.edu/~jrus/Site/Cocoa%20Text%20System....