In Unity 2.6, when a CharacterController was moving vertically and struck a corner it would slide up and around the corner. However, this behavior seems to have disappeared in 3.0. Now when the CharacterController strikes a corner while moving vertically it gets stuck.
Is this a known issue? Is there a simple way to re-enable the old behavior?
So, we did a lot of refactoring of the CharacterController code in 3.0, because there were previously many behaviors people we complaining about. This specific behavior was indeed intentionally changed, because users where complaining about it, and it is inconsistent with the behavior of pushing down against a slope (which never cause the Character Controller to push sideways).
While there is no built-in way to get the 2.0 behavior back, you should be able to implement it yourself, by checking for ceiling collisions in your character controller script, and moving the controller sideways based on the direction of the normal received when you register a hit.