There are more details on the Symbian website. Basically it doesn't change that much. Developers (the big ones) can get the same access to the source code that the likes of Nokia and Ericsson get. The ordinary person (you and me) dont see any change. But people like Superscape (developing a 3d engine for Symbian do). I guess the intention is to encourage developers and help them out as mcuh as possible.
Remember: The search command is your friend.
Feedback wanted: PM, email or post with your suggestions, complaints, feedback.