Just there last week. It was on one of the sold out dates, but it did not feel crowded at all. We were able to stay on Peter Pan's Flight and Pooh for as many re-rides as we wanted, as no one was waiting in their lines.
Had a wonderful time, rode the Fantasyland rides over and over, lost count of how many times who rode what (7 people of different age groups). The breakfast at Pinocchio Haus was hot, plentiful and good. We ate at 9:40 and the CMs loaded us down with lots of extra bottles of water and juice to take with us.
I got a survey from Disney today about the event. One of the questions was what we liked least about the event, one of the multiple choice answers was park felt too empty, I didn't pick that one. I did suggest that for the last hour of the event, from 9am - 10 am, that the wristband should operate as a Fastpass for any other ride in the park as the event went on until 10 am but the park opened at 9 am, so not so exclusive access from 9-10. But this did give us a huge jump on the crowds for Haunted Mansion, BTMR and Splash as we were already deep in the park by the time the first crowds stormed Main Street.
One sorta bad sorta good thing that happened during our Extra Magic Morning was that 7dmt was having problems, so they told us our special EMM wristbands would be good for the 7dmt ride until noon. Some of our party had already ridden the mine train a couple of times before it went down. So that gave us more time to ride the other rides and eat before 10am. Then those who wanted rode mine train over and over in the Fastpass line until noon. I think 2 of the boys made it to 12 times prior to noon.
One of our best vacation experiences that gave the entire group from baby to grandparents a good time. Plus we skipped lunch that day as we had really eaten well at the breakfast buffet - man, those boys can eat bacon!