Realtime desktop like web apps

I am interested in building a realtime desktop like app (something which gmail is good at), So I am interested in knowing what are the options, I am aware of socket.io and XMPP but still what is your suggested option when we have lot of traffic and data to push to client.

Also is Gmail using XMPP for开发者_运维百科 pushing new mails to client?

You may want to look at this blog post : http://blog.superfeedr.com/realtime-web-technologies/ that I wrote a couple weeks ago.

In a nutshell : it really depends on what exatcly is that that you're trying to build. It is also important to understand how "verbose" would be the communications that you mention : 1 message/sec or 1 message/day.