Chipmunk Physics

That's good to hear, because I suspect JavaScript will become (remain?) the language of choice for cross platform mobile applications in the future. I think platforms like PhoneGap are only going to become stronger. I look forward to using your library on iPhone and Kindle Fire.

For now I'm only focusing on getting it complete and stable, but I'll probably try that if the vector operations turn out to be performance hogs. I don't think they were the bottleneck when I profiled it a while ago, but that could easily change with time. (:

For my webgl engine, keeping a vector in the form {x: 0, y:0} vs a native array, say Float32Array(2) or even a plain array was a huge difference. The accessing time for named properties is much higher than plain index on an array. And keep in mind that I was only assigning and storing positions, doing math and more frequent access/write to those objects is going to give you a huge performance boost. If I have some time, I'll make a quick test on my fork to test that.
Anyway, keep up the good work!