We did the Evening Magic Hour at MK on 5/11, and at Epcot on 5/12.
MK was crowded early, but quickly thinned and we were able to hit most things with a small wait. Probably 5 - 10 minutes in the most extreme cases. This was perceived as a plus since many of the same rides earlier had extreme wait times of up to 70 minutes, which we refused to do.
At Epcot, we decided to do this at the last minute, so after the fireworks, we took the kids over to Imagination (no wait), and then we quickly went into the Living Seas to find the penny press machine. If you've ever suspected that the hydrolaters are faking it, there is no doubt about their functionality during EMH... We then decided to see Turtle Talk while we there. It was a much bigger line to wait than we had seen during the normal daytime, but we made it into the next show. After all this time, we figured we could take in a quick Soarin' event, but by this time it was after 11 already, and the pavilion seemed to be packed judging from the amount of people still pouring into the building, and the number of strollers outside. The only time we did Soarin' was at an Early morning session. I haven't seen that place so busy since 1985.... We decided to leave since we hadn't prepared the kids for the evening...