Coming in 2.2.0: Integrated voice chat.
Tigerclaw, who I've never heard of either-- is he a dev? He says he's "in a whole other building than the CMs"-- has bad news for all of those Teamspeak and Ventrilo hosts. Apparently come 2.2.0, you won't need to run any extra programs, as players will be able to speak to each other via the normal client. Tigerclaw also says a PTR for the patch is upcoming, but he definitely does work for Blizzard: he doesn't give any clues at all as to when this might happen.
So let the rampant speculation begin! Lately I've been playing a lot of the Halo 3 Beta (traitorous, I know), and I love the way voice works in that game: you can push a button to talk over a radio to your whole team, or just speak into the mic without pushing anything, and only players near you ingame will hear what you're saying. I doubt WoW will be that complicated (not to mention that a lot of players don't like that "feature"), but it's a cool effect, and here's hoping Blizzard comes up with some interesting ways to use voicechat onward. What if Hakkar's whispers were heard only in your own personal voice channel?