My girlfriend and I were waiting for our table there on the Friday after Thanksgiving, and we were amused at the number of people trying to walk up. One group must have had 8 or 9 people in it.... I mean, really people, think that one over the next time you decide not to make reservations for one of the busiest days of the year! The mother of another family got really upset when they were turned away, and she began to yell at her son for delaying them. Apparently, at 5.30 they felt they would have been fine walking up, but at 6.00 it was too late and it was all his fault! I felt bad for the kid, he was basically being told that if he wasn't so committed to having fun that day, they could have made it to dinner, which of course is both antithetical to the spirit of Disney and from what I witnessed, completely untrue.
Short answer..... either make a reservation, get right with God (I mean, really, really right... it wouldn't hurt if you had a regular squash game with the holy spirit), or else don't count on it.