I've been for the last few years. Nice event. Great to see so many Mini's in one place.
Watch the mickeyandmini.org site, or maybe the Sunshine Minis forum (that's been pretty dead lately, tho), for announcement of when/how to register/book rooms.
You book the rooms directly with the resort, but need to wait until they get the group booking set up to get the event price.
Registration for the event is thru the mickeyandmini.org site, separate from the room booking, and you can order T-shirts, etc for pickup when you arrive.