[edit] just took a closer look at the network activity. this really is the worst way to implement this feature. polling several times a second, sending back a bloated response, and updating much more of the DOM than necessary. this is just terribly hacky. probably done very quickly at the last minute though.
[1] http://techcrunch.com/2010/04/14/apparently-mark-zuckerberg-...
This excerpted anecdote indicates it was mainly a leadership gesture to rally the troops. Still pretty cool that he'd bother, though.
Not really. Between Firefox and Chrome's market share, the "right way" is far more in line with WebSockets. Facebook doesn't use WebSockets. It's not even an issue of browser support but rather the lack of proper progressive enhancement on Facebook's part. Also, sorry, but I laugh at the notion that "long polling is easy to implement". Even if it is on some level, it doesn't make the right strategies any harder (nor does it excuse the flaws or performance issues of current long-polling techniques), nor does it excuse the lack of progressive enhancement.