J.B.
I'm running off of memory here, (Dec 2009) and if I recall it is mainly just a parade, with snow, free cocoa and cookies. It is extremely packed. It is held at the end of the day on main street. I'm not sure what rides are closed or open because everyone is on main street during the 'party'.
You have to purchase a separate ticket and you're given a wristband. At the close of the day the staff begins ushering everyone without a wristband to the exits and those with a wristband stay on main street.
We planned it so Magic Kingdom was our late day park for that day. Because you won't get out of there until midnight or later.