I am shocked at the couple of responses saying the Friday after is OK. That has not been my experience the last two years. The last two years were wall to wall on Friday. (At least the Magic Kingdom). This year we are leaving late on Thanksgiving day to avoid the Friday after.
Black Friday 2010, went to MK at rope drop, rode Space Mtn several times(probably around 4-5 times) during the day and every other ride we wanted. Left the park at 3pm to head to MCO. Not bad at all.