We were there from Jan. 16th to the 20th and used the Extra hours at night. Now, I realize this was a little slower, but still seemed a little crowded. We rode Test track 6 times in a row, the last 2 they let us stay on because there literally no one in line- I mean not one person. Same for mission space. At Magic Kingdom, SM had no wait and we rode 3 times, along with BTM 2 times, SplashM (cold......) 2 times, Pooh once, Mickey's Philharmagic, haunted mansion, snow white, Peter pan-which actually had a 20 minute wait (the only ride to have a wait which I thought was odd)
We also used it for Animal Kingdom-the safari was not open because it was dark, but Dinosaur, Primeval whirl, Tarzan Rocks, Festival of Lion King were open with no wait, little crowd. My DD6 played at bone playground for a long time and there only 2 other families in the whole area-she loved it. There was also lots of characters everywhere with no lines. We absolutely loved it.
Now, it was cold those nights like 40's, so maybe that kept people away, but I hope it stays this way. They do not have a way knowing if you let someone else get wristbands. They looked at our room key and put the wristband on. We could have easily let anyone use the key. Now, every attraction was absolutely adamant that we had the wristbands even DD6 had to show it every time. I was glad because I know I would not be happy if regular public had this privilege.
My big concern is how they can keep doing this if there is so few people using the privilege. How can they make any money on it? At Epcot they had a "Special" bus to take the last few people back to their resort, there was just no one around.
Kind of makes it hard to plan for my trip in May. Does anyone know if they are eventually planning on going to a set schedule for parks open in the morning and evening for the program??? 
