This is one of the coolest things ever. Following the KDE groups snivveling Apple has now gone the extra mile and fully opened all of WebKit. For those of you who don't know, WebKit is the rendering engine used by the Safari web browser that comes with Mac OS X. WebKit itself is a fork of Khtml, which is the rendering engine used by KDE's Konqueror web browser.
Apple opening up WebKit and full cvs access means you can build your own version of WebKit, and have access to all of the advance features before it's officially released as part of Safari. In fact, I'm typing this into a WebKit that I built on my laptop this afternoon. Schweet.