No word yet on if players with current 310% speed mounts will still have to learn this new rank of flying skill or not. Previously, 310% speed mounts were seen as status symbols and prizes to be gained via achievements, PvP, rare drops or so on. Personally, I'm hoping people with 310% speed mounts are at least grandfathered in as it would be annoying otherwise to not even be able to ride your mount once the change went live.
On the up side, at least we'll be able to fly in Azeroth right away instead of having to train yet another rank of flying.
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.