We heard about this last year at BlizzCon but Zarhym has reaffirmed that Cataclysm will not feature any new capital cities that are considered a sanctuary. There will not be a new Shattrath or Dalaran. I personally believe its safe to assume that the present faction capital cities will see a few facelifts. Maybe a small cave in or something at Ironforge? Perhaps a toppled tower in Stormwind?
I'll be happier for not having to share city space with Horde players. Actually, now that I think about it, no more "Lagaran!" Perhaps I won't disconnect every once in a while when I fly in to the city during peak hours. For me, I'll be running circles around the Stormwind bank steps. But since Dalaran has portals to all the major cities, it wouldn't surprise me if it continues to be the major transportation hub of choice for players looking to travel around the world.
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.