Magical Express Experience:
Here are my experiences with Magical Express. We booked our package with Southwest Vacations
travel agency. We never received our luggage tags. But the travel agency gave us good instructions on how to use Magical Express without the tags (proceed to the ME podium). We flew Southwest Air (SWA), which is not a participating airline. We arrived on May 14, but had a friend pick us up from the airport. So we did not use Magical Express that day, nor had our luggage expedited by ME. We did see the ME employee with big white hands very easily after deplaning and proceeding towards baggage claim.
On returning home, we scheduled our ME bus to pick us up. We were surprised that it would arrive 3 hours before our departure! This was on a Wednesday afternoon, so we did not understand why we had to leave so early. ME insisted on that time (see SWA experience below). We had bought an extra day ticket to spend a morning in the park, but we could only spend 2 hours in the park because of the early pick-up by ME. ME arrived on time at AKL. We took our bags on the bus. We then went to Coronado Springs and filled up the bus. Because most people did not have luggage, they loaded fairly quickly. We left AKL at 11:50 and arrived at the airport by 12:45ish. So overall, I would say ME is an overall positive experience, especially cos it's free.
Southwest Experience: 
On the way back home on Wednesday May 18, we had to check our own luggage in at the counter with Southwest. Southwest check-in is awful at Orlando airport. I wish Southwest would have been part of the ME program and we would not have had to wait an HOUR! to check-in. This wait was only to check our luggage. The wait to go through security and the metal detectors was only 5 minutes. We asked Southwest if this was a regular occurence, and they said it was all the time. Moreover, only about 1/2 of the counters were staffed. I'm in the process of writing Southwest to complain about the terrible service. On top of that the Southwest skycaps were soliciting bribes (I saw 2 families pay $20 and $50 respectively) to be bumped to the front of the line.
Suggestions: Do not check luggage with Southwest. Then, you can check yourself in at the self-service check-in computer (no lines for self-service). Also, use Southwest Airlines's web site to "check-in" and print a boarding pass before going to the Orlando Airport. I don't know where you can do that in Disney, but it would mean you don't have to stand in line.
Thanks to all who posted before I left on my trip. It helped me understand how Magical Express (ME) was working.