Not yet, but in the near future. It would be awesome to run the tests of projects automagically when a dependency is updated! :)
Cool. That's the whole point of continuous integration. Everyone knows that their own stuff passes; it's "does this change break other people's stuff" that's hard to determine.
This is something I've wanted to set up for a long time. Let's chat on IRC some time?
Sure, you can find me in #travis on freenode, my handle is josh-k :)