I am building a small chat application for friends, but unsure about how to get information in a timely manner that is not as manual or as rudimentary as forcing a page refresh.

Currently, I am implementing this using simple AJAX, but this has the disadvantage of regularly hitting the server when a short timer elapses.

In researching long/short polling, I ran across HTML5 WebSockets. This seems easy to implement, but I'm not sure if there are some hidden disadvantages. For example, I think WebSockets is only supported by certain browsers. Are there other disadvantages to WebSockets that I should be aware of?

Since it seems like both technologies do the same thing, in what sorts of scenarios would one prefer to use one over the other? More specifically, has HTML5 WebSockets made AJAX long/short polling obsolete, or are there compelling reasons to prefer AJAX over WebSockets?