We were there last week and planned on going, but we were too tired to go. But my friends son and his 2 friends (all age 17) went. They said it was great they went on everything several times and stayed the whole time. In fact they didn't go to any parks that day, so they used a whole days ticket for EMH and they said it was worth it.
We were there... only lasted until about 1:30am though! All the EMH nights last week were very crowded including the MK on Wednesday. Even at 1:30am when we left, Tomorrowland was a zoo! We were able to walk onto Splash Mountain with no problem though... I think people didn't want to get wet that late at night!