We stayed at POR (first visit to WDW) in February. We did not have a car and visited both Seaworld and Discovery Cove using Mears shuttle. Very different result for each trip.
First trip (DC) was fine.
Seaworld was a different matter. The Mears transport did not turn up at nine as arranged. Having waited for sometime the baggage/porter manager asked if we had a problem. They let me use the phone to ring Mears who said there was a large coach there on time; there wasn't because we were there 15 mins before pickup. They said a van would be over in 30 mins.
I explained this to the manager....he obviously had seen this sort of thing before (said they are always doing this) and he phoned Mears to tell them that there had been no coach there that morning and after some he arranged for a quicker pickup. Nothing came, he was back on the phone and had Mears sent out a Cab which was there in about 5 mins.
Mears tell you to ring them two hours before pickup when leaving the attraction concerned, we did that but made no different, we had to wait for for almost an hour with loads of others and 4 vans turned up at the same time.
We are going back in May to Wilderness Lodge and Animal Kingdom lodge and I am not sure I would use the Mears shuttle again...not sure yet it might have been a bad day for them!
However, the general views I have seen on the net have not been to generous to Mears. The ironic things is, the baggabe manager at POR said that Mears have a monopoly on transport for Disney and although there a few private cabs, almost all the cabs are owned by Mears as well!!!