Javscript is an implementation detail: this is the same old Google trap.

+1

Exactly. Our company's product has a rich Web 2.0 client that's written in JavaScript and runs in the browser. It's in fact several megabytes of our code, along with YUI and a couple of other libraries. Not only was the improvement "not insignificant", it was huge enough to change the initial application load from "unacceptably slow" to "usable". (Sorry for not having the numbers here. I could do the mesaurements, but I'm quite sure you'd find some paper on this after a minute of googling).