How hard would it be to build a syntax coloured theme editor plugin for WordPress? Would it be a useful thing to have?
Personally I get bored when using an external text editor as I have to save in that, switch to my FTP program, upload the file, and switch back to Firefox to see the result. Working straight into the Theme Editor is much faster, as I just switch between that, and another tab containing the page in question.
What do you think?