I have problem with this presentation - it doesn't seem to contain too many details. What mobile, what browsers, what 3g networks, etc.

Sure, there are issues - Safari (I think) used to crash when you opened inspector on a page with ws.

Some (meteor.com) just ignore all those issues by disabling native ws altogether. Performance of polling SockJS transports is enough for them now, so why bother?

If you find a real problem with SockJS in the wild - please do let us know!

I'm using sockjs right now with polling, so don't get me wrong, I'm with you. I'm thinking about experimenting with turning on ws so that was the source of my question. I'd appreciate it if it could be addressed. Thanks.

In theory v1.0 of socket.io will fall back correctly if blocked, as it will be based on engine.io. This is what I last recall, as I've had other problems with socket.io and clustering - I've just moved on to pure engine.io going forward (and loving it).