As web applications become increasingly smarter and powerful, we start to spend more time in a browser window than in any other desktop application. MS Office-replacement suites like Google Apps, are first to come to mind, but there are many other cool apps. Web-based collaboration is especially web-centric. Wikis, blogs and community sites are all authored using text-areas in a browser. In most cases a WYSIWYG editor is provided. Geeks like us, however, prefer to mess with raw code (HTML?) directly. Nice and dandy, but then you are stuck with boring black-on-white listing. Or maybe not...
P.S. I am going to look-around if anybody has already integrated it into Drupal and if not - you bet it is going there ;)