LESS fiddle script/page
NOTE: there is a minor issue with the CodeMirror editor, where typing an ampersand in certain cases causes the editor to become unresponsive. You may work around this by undoing the typing of the ampersand and copy another rule that already has an ampersand.
You can try it out here (note: uses rawgithub): http://kzantow.github.io/fiddle-less
And here is a Powerpoint presentation I gave about LESS: http://kzantow.github.io/fiddle-less/Using%20LESS%20for%20better%20HTML.ppt