Yep, we went a few years ago and the morning was great. But by about noon, the crowds were much bigger and we ended up staying until about 1pm before going back home. It wasn't as bad as the week between Christmas and New Year's, but still crowded by midday.
My sister and I went last year and it was just like PPs said. We got there at opening and it was great it got busier as the day went on. We had to leave around 1 or 2 anyway so we left as the bigger crowds were coming.
We were there Jan 1st 2008 and I found it to be very,very,very crowded. We arrived in Anaheim around noon. Although it was very crowded, the wait times for rides were not as long as I expected.
Like my sister said, I couldn't believe how many people there were. Morning was nice. Even the Blue Sky Cellar had a line to go in! The courtyard between the two parks was filled with lines from the ticket booths, just a sea of people. There is some hope for this year. Last year we had APs and were able to go that day. This year I noticed it is blacked out for APs. So, maybe that will help with the crowds. We saw many people there to activate their new APs they probably just got for Christmas. The line at the AP center looked to be at least an hour wait. I had wanted to add parking to mine that day but decided to forget it. Anyway, it will be interesting to know how it is this year with APs blocked out.