To get the ball rolling, I do have a little side project I'm working
on for unit testing. It's based on jsunit and also borrows the record-
playback idea that pymox does (http://code.google.com/p/pymox/wiki/
MoxDocumentation). You can run specific unit tests through Firefox
chrome and there's a convenient "restart Firefox and run" button. I
could demo that.
Maybe someone else could talk a little bit about a Mozilla labs
project, like Weave or Ubiquity?