I want to do something very similar to Google Doc\'s live updating - where all users can \"immediately\" see the actions of the other users in the doc.
To achieve this,
If your users are only using modern browsers than i would try out the websocket standard coming with HTML 5. More and more browser will support it in the future and companies like Google and Apple are working on this. Here a getting started tutorial: http://net.tutsplus.com/tutorials/javascript-ajax/start-using-html5-websockets-today/