"most browsers"?

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.