We went last December 7th, a Tuesday. It seemed quite busy along the main thoroughfares, packed to the gills even, but we practically walked on all the rides except early on in Fantasyland, where we waited a whopping 15 minutes to get on Dumbo. The first parade was very crowded along Main Street so we watched it from Frontierland, in front of the Shooting Gallery and were right up against the rope with a great view. Oddly, when we came back and checked the boards, several people were complaining about how crowded the night was and how they waited an hour to get on all the rides so I don't know, it's all about perception I guess...
I have also heard that Fridays are more crowded than the earlier days of the week but I wouldn't expect it to be quite as crowded as later in the month.