I've used this for an internal bootstrapping script and it was great. Super nice API and it looks better than any prompts I've attempted building on my own.
I saw a tweet from Jonathan Hoefler sarcastically saying he loves when the Gmail team uses pirated versions of his font online, or something to that affect, but it appears he has deleted it: http://twitter.com/#!/H_FJ
why don't you let your IDE organize your selectors? As mentioned above, CSS Edit does a great job with this. With it, you get the readability of the latter formatting system and the scanability (not a word, I know) of the former system.
I kept trying to tab to format my CSS and accidentally went to the preview. That might be for accessibility, but I'd like to ability to Tab the textarea.
Also Syntax highlighting would be great, but I like the simplicity of it. Don't worry about showing any of the existing css.