I have seen many websites (facebook or stack overflow for instance) that will update certain features as new data is generated (new answer on a post for example).
You can use HTML5 SSE. But that's not a very good solution.
You can use Comet server that helps in Long AJAX polling. Check out the Ajax Push Engine (APE). It's a combination of Comet Server and a Javascript framework to make AJAX-PUSH or real time streaming possible.