We have been at MK twice the day after Thanksgiving, and it was very busy, actually more so than on Thanksgiving Day itself. I think people feel it will be busy on the holiday and avoid it, and then come the next day. When we did Thanksgiving Day we got there early, got things done, and scheduled dinner at 1900PF to be out of the park (and see the giant gingerbread house!) in case it was busy, but did end up coming back in for night activities. The second time we got lunch ADR at LTT, so again we had our meal and could leave early if we wanted, but it was not necessary. But on Black Friday, we had a Prepark opening brft at CP, and when we came out, it was just opening, and a wall of people were coming at us, I took photos beforehand as well on the empty Main St., and the after photo is striking. I would probably pick a different park, but with Sat. being a usual busy day for MK and the start of FD for some, that may be worse. If you go Fri., I would be there at RD, with a plan for what you want to hit, and have your FPs for early afternoon and try to get 4th after, or take a break and make them for evening when you return. You could also get things done in the a.m., then hop to another park if it is crowded later. The parks generally get less crowded starting Sunday, as we have stayed till Wed. before, and it is definitely calmer after the weekend. Check out Josh's easywdw site if you haven't for his recommended parks on those days - he rates the best to worst, and gives his reasons. You may want to wait to go there for the first few days, but I know some people can't!