The introduced a lot of tools, mostly around Firebug and its extensions. I wasn't familiar with the unit testing stuff in that space: Code Coverage and FireUnit. Some of the more interesting tools were the CSS tools: YUI CSS Grid Builder, blueprint, and the recently announced Microsoft SuperPreview.
They also mentioned some "future" tools like Bespin and Thunderhead. Bespin is wonderful, a source code editor on the web, with concurrent-versioning system support (git now and later SVN?). I really feel like this is boostrapping the web, you can begin to think of creating the web ON the web. Avi Bryant has already plugged Seaside into Bespin. Thunderhead is a prototype for marrying grid-layouts with the HTML 5 canvas. They are talking about doing an "Open Tools Directory".