Ozh of PlanetOzh.com has a great post filled with tidbits of information he has gathered from mining 54 different WordPress releases ranging from 0.7.1 to 3.0.1. Not surprisingly,
WordPress continues to have more functions added to it as time moves along. As of 3.0.1, WordPress has 3,240 PHP functions defined. Based on the graph published by Ozh, it looks like 2.7.1 to 2.8 had one of the largest increases of defined functions.