Working on the Quick Reply Editor, I have replaced a number of icons (see image below) with Font Awesome Icons. Was planning to replace all of them, but for some reason, replacing a few of them causes the script / template to break (which is odd) so I left them for now.
The tooltips work better with Font Awesome than with images, so I hope to replace all of them at some point in time.
I'll probaly have to rewrite the PHP code for the custom icons like code, icode, and noparse tags to them them to work with Font Awesome.