I did night EMH at Epcot, MK, and the Studios 2 weeks ago while I was there. Yes, it was still crowded during the first hour and a half or so, but after that, the crowds quickly thinned out. The EMH at MGM was til 1am, and I didnt get to the park til 12:15, after being at the MK that night, which closed at 12am.
The streets were still pretty crowded with people, but dont let that fool you. I was able to walk-on Star Tours, and ride Tower of Terror 3 times in a row with no wait at all, even though the posted wait time was 40 minutes. I did all of this in less than 45 minutes. I would highly reccomend doing night EMH, but if you are not one who likes to stay in the parks til 1 or 2am, when crowds are lighter, or have small children (even though many did bring their crying kids)

then it probably isnt worth it to you.
I was also able to go to two different MK night EMH, where the park didnt close til 2am, and the crowds really started to dwindle around 12:45am. I was able to do Big Thunder twice in a row with no wait, and Splash 3 times in a row with no wait, as well as many other attractions in the park, like Buzz and Philharmagic. It was worth it to me just to be in MK at 2am, and be able to walk down an empty Main Street after the park had closed and actually be able to hear the music and see the sidewalk
I did EMH 5 nights during my visit to the World, at every park except AK, and each one exceeded my expectations. I just might have to stay at a Disney Resort a couple of nights when I become a CM in a couple of weeks, since EMH is for only resort guests

It is THAT worth it for me, IMO
