I'm currently working on a similar project, well, I should say, continuing to work on.
My main aim is to provide next to real time remote monitoring, alarming and trending of a remote site and while I have it working well via traditional HTTP protocol I have been playing around with publishing from the Arduino to PubNub which clients can subscribe to.
I intially tried SSE, (Server Sent Events) but that doesn't work from my standard hosted site.
I have Nod.js on my mac but again I can't install it on my hosted site either.
I made a small test the other day where the Arduino publishes data to PubNub, works quite well.
The data from the Arduino to PubNub is still HTTP, but the cleint side is using server push technology.
I would like to see that it may be possible to send from Arduino to PubNub via UPD, but that is not available as yet.
The beaut thing with this topology that it is designed for fairly high throughput of data on a one to many relationship.
And it is just what I need for having alarm conditions being sent without polling.
Take a look at PubNub, especially the developers section, http://www.pubnub.com/developers
Would be interested to learn more about what it is you are wanting to do.