I spent the day learning and hacking with extjs.  Man, this is a tasty bit of bacon!  My goal is to create an organizing web app to hang inside Prism, such that I can display all the Mozilla goodies we're putting into the Mozilla Developer Resource Kit.  So far so good.  I've got the layout done, and I'm working on getting a JSON-based dynamic tree generated, representing the source tree.  I just have it running locally so far, but you can get a sense of where I'm going with this.  Eventually I want to mash MXR, MDC, bits of XULPlanet, and a bunch of other tools and resources into one app, with accordion tabs and trees to make it possible to navigate through it all.  As it gets closer to 'usable' I'll stick it on the web for people to try and so I can get proper feedback.

Two thumbs up for the extjs team!