I'm going to start a brand new HTML5.0 project for mobile device, and my question is simple, why makes you choose Node.JS, in front of PHP or Java or Rails for Backend.

I plan to use Express, Backbone.Js, MongoDB / Redis, if i choose Node.JS; but i don't know (for now) these technologies and it's not a time waste to learn these !

But in front of traditional languages such as Java, PHP, what could help you to start a project using Node.JS & Co.

I've heard lots of (old school) dev, that says : Hey JavaScript on server-side pouah ! you're a silly boy ! Javascript is for Hide/Display divs only, etc... !

Yes, in fact i don't know how to convince these developers that Server-side js, is cool ! it's legend .... wait for it ... dary !
If you have more args, different from speed, I'm ready to listen !

In my opinion, it's good idea simply in the fact that there is only one language from Frontend to Backend, vi JSON. But it's not enough !

Thanks in advance.