With the Classic Beta branch updating to version 4.4.0, the first round of Cataclysm Classic datamining has begun, including all of the new expansion features and revamped world zones!
Though no official date has been given for Cataclysm beta testing, this would appear to be the first step to its arrival. Most of what has been discovered so far in the first round of datamining are expected additions, such as updating the world zones, reputations, Goblin and Worgen races, dozens of mounts, and a slew of new features.