I have been to MK on Halloween Day twice, 2010 and 2011. The reason you are seeing a variance in crowd calendars for that day is because some may tell you not to go there due to the shorter hours that day...they think you may feel like you wasted money going there to only be kicked out at 7:00. Other calendars recommend it because so many guests use that early close hour as a reason to go elsewhere that day...why go to MK when I have to leave at 7, when I could go to Epcot and stay til 9 or later?
I prefer to go to MK on a day they are hosting a party or closing early for some reason, because of reason #2 above! It is FAR less crowded on those days! We always arrive to MK at least 20 min before rope drop, and on those party days the crowd waiting to get in is minuscule. We walk on to all the big rides, and find really reasonable waits throughout the day. FP return times aren't pushed out too far, like many of the days surrounding it that are nonparty days.
We have also gone to MK on days around Halloween that were also party days. Halloween Day was a little bit busier than the other days we went, but really, really manageable. That day's party will sell out, and many people start coming in for it at 4:00. Main Street is a madhouse from 4'ish on, but inside the park really isn't busy at all by that time. Ride waits between 5 and 7 are really low, as most people that aren't staying head out, and those that are staying are finding something to eat so they can get in character lines early. It really is a good and fun place to be on that day!
BTW, I second the easywdw rx above! Been using his info for a couple of years now, and his stuff is good as gold
