I'm developing a Web/AJAX application that replicates the majority of features available in a certain niche class of desktop apps (I'm avoiding detail here because I don't think it's relevant enough to plug myself. ;] ) with the exception of voicechat, which I can't implement without using a browser plugin. Voice is by no means ubiquitous in the industry, but the people who use it swear by it and refuse to do without.
A comment I receive fairly often is "This is nice, but when is it getting voicechat?" It's irksome, because if I was using a platform like Java or Flash the entire application would be leaner, quicker, and easier to troubleshoot.
But with HTML5, it seems like receiving the audio would be feasible. Google and I haven't found anything pertaining to recording and transmitting audio, and I'm guessing that part can't be done, but what of the future? If anyone knows about the nooks and crannies of HTML5 or even what's speculated for beyond the upcoming standard, I'd appreciate it.
http://www.whatwg.org/specs/web-apps/current-work/#video-conferencing-and-peer-to-peer-communication
From what I've read, the element described in this spec is what you're thinking of.