Recently, I have come across many examples of truly “real-time” protocols as opposed to Event-firing or timer-initiated AJAX requests.
Some of the things you can do with this web technology are truly impressive. First of all, you don’t need to make needless “checks” to the datastore to make sure that data has not changed.
COMET is a web technology which “PUSHes” instead of “PULLs”. Best of all, there are some open-source projects which are freely available!
Is one of them, which has good documentation and the demos are really impressive, particularly the Twitter one, check it out!
Code Repository 