When I was doing a fair bit of Ruby I often used the TextMate's shortcut (Ctrl+:) to convert a Ruby String to a Symbol or a Ruby Symbol to a String. It's something I've periodically missed while doing Clojure, and yesterday I found myself in the middle of a refactoring that was going to force the conversion of 5+ Clojure Keywords to Strings.
The following emacs lisp is my solution for toggling between Clojure Strings and Keywords. The standard disclaimers apply - it works on my machine, and I've never claimed to know emacs lisp well.
A quick video of the behavior: