There's been quite a burst of blue posts on the official forums post-BlizzCon; some by World Event Designer Kisirani talking about lore and the post-Cataclysm world, some by Lead Systems Designer Ghostcrawler talking about new game systems coming with 4.0, and some by the Community Managers, providing slightly less meaty morsels of information. It's not all chaff from the CMs, though -- there's some wheat in there.
Bornakk, for example, stopped by a thread asking about how heirloom items will work post-80 in Cataclysm. He said that there are no plans to extend the experience bonus they give past level 80, though there may eventually be new heirlooms available to help bridge that gap. That's not surprising, really -- if they were extended, heirlooms would essentially be mandatory for the people racing to get to 85 first, and that's a situation Blizzard would like to avoid.
Interestingly, he also noted that it's "unlikely" that heirlooms won't work on Worgen or Goblin characters, which is admittedly a relief, seeing how I just bought a set of them for my Worgen Warrior. Battle Howl, anyone?
World of Warcraft: Cataclysm will destroy Azeroth as we know it. Nothing will be the same. In WoW.com's Guide to Cataclysm you can find out everything you need to know about WoW's third expansion. From Goblins and Worgens to Mastery and Guild changes, it's all there for your cataclysmic enjoyment.