We went Monday and stayed the night. Got there about 5pm yesterday and it was so empty! We've had annual passes for a year and a half now and have never seen it so empty. The only area that was really busy still was Fantasyland, but even the Peter Pan ride (which is usually a long line) only had a 20 minute wait.
Went back today and again it was really empty in the park. We walked onto Space Mountain. Literally had about 15 people in front of us and waited about 5 minutes to get on, and that ride usually is at least a 30 minute wait and can get up to an hour and half to wait. The other rides were the same - practically walked onto the rides and the longest wait was 5 minutes.
Hope you have a great time - it seems like this week is a wonderful time to go!