We go the first week in December every year (my birthday too!). This past year was a lot more crowded than ever before. It was a Thursday, which is supposedly a "down" day. Usually we walk on rides, have no problem walking around, food lines are minimal, and the shows are not that crowded.
This past year was such a difference! It was busy from the moment we got there (an hour early) and just got worse as the day went on. People got parade spots 3.5 hours early!! Just not what we were ever used to.
I think there may be something to this 1 million people annual pass theory. As an AP holder I have been very surprised in the difference between this year and 2 years ago.