We went November 20 and I didn't feel that it was overly crowded. It WAS more crowded than the Pirates Princess back in January 08, but that was all I had to compare it to.
We went to Twas the Night first thing since I'd heard that can be pretty tough to get into....we stood in line about 30 minutes before the show and there was maybe 20-30 people who got there before us....we sat in the center section second row (first row was roped off or we'd have been there).
We saw Tink and friends with maybe a 15 minute wait....then hoped the rope because there was no one coming and saw the Princesses within minutes.
We saw the parade, fireworks, Beauty's storytime, got the terrible hot chocolate/cookies, got lots of character interactions, spent way too long at the dance parties (I'm old, lol).....and went on a lot of rides, often with a longer time spent walking through the que than waiting in it. We rode Pirates twice without anyone in our boat or the boat ahead/behind us.....it was pretty cool being all alone, lol.
The parade crowd on Main Street was definitely thick, but we stood behind a family that was sitting, so we saw just fine and got great photos. The fireworks crowd in front of the castle was also pretty heavy, but everyone where we were was sitting on the cement, so while it was cold on the bottom, the view was unobstructed and wonderful.
In reading all the advice on the various "guide" websites, we chose to go early in our trip, because they all said the closer you get to the holiday the more crowded it would be and reading DISers, sounds like they were right.
I had actually budgeted to go a second time in case we couldn't get everything done that we wanted to......but we decided there was not enough that we wanted to do again to justify the expense. Instead we had two TS meals that we hadn't planned with the cash, lol.
So my advice.....go early!