For those that think JavaScript makes a good VM format for the web, I've written a couple blog posts recently on this topic:

http://chadaustin.me/2011/01/native-client-is-widely-misunde...

http://chadaustin.me/2011/01/digging-into-javascript-perform...

Basically, we need another 10x to 30x in performance for JavaScript to match native code performance...