While working on the new Mt.Gox, we've been considering implementing websockets natively for everyone (with a fallback on long polling if not available).
Around 44% of our visitors in the past 30 days have native support for websocket (Chrome, Safari), and another 45% can enable it in their browser quite easily (Firefox+Opera). The remaining major part is MSIE, which should have support in near/less near future
[1].
Since people in here have more of a technical background, let us know what you think (just spare me the usual "websocket is bad, use direct sockets" - we need something that works in web browsers... and check the new websocket framing in -06 and better first, it's no longer some weird \xff).
