I believe the new rule is that if you arrive to MCO after 10 pm, you are responsible for your own bags.
Not necessarily true. What they told us (because we figured to be checking in around 1:00 AM... we actually checked in around 4:00 AM) was that they don't deliver bags to rooms between 10 PM and 7 AM.
I'm not sure when the bags are actually delivered to the hotels; I read somewhere else that someone actually called down at 7 AM to get their bags delivered, and that they were already at the hotel. This may indicate that they actually pick them up all night; again, though, I don't know.
In retrospect, we made the mistake of not using ME for the bags. We picked them up ourselves, and then had to walk to the exact opposite end of the airport to get the ME. Meanwhile, we had packed a change of clothes in our carryon luggage, and weren't up until past 9 AM the next day. We don't plan on going down that late at night again. This time, we hadn't bought our plane tickets until less than a month in advance, and it was much cheaper to go on that flight ($240 cheaper flight, $300 more for the hotel plus meal plan for the extra night. $60 was well worth it). We're already planning the next trip in October 2010, so we'll have our pick of flights.
My advice is to try to pack a change of clothes, toiletries and whatever else you'll need to carry around the park in your carry on bags, and let the ME pick up your bags that were under the plane.
EDIT: Reading the subsequent posts, I guess it's a good thing that we got our bags!