We stayed at the doubletree in 2000 and the transportation was so-so. You really need to leave plenty of time to get where you want to go because you have no idea when the busses are going to come.
If you want to go to a water park, I suggest using a car if you have one. There are supposed to be certain times when a water park one comes, but for us, it didn't come, and when we went to go and ask if it was coming, they were no help at all. We had to call a mears shuttle to get us there. To get home, I know we hopped on a disney bus to go to downtown disney and get a bus from there. ( i don't remember if we didn't want to wait for the bus to come or if it wasn't there) At DD, the busses are not as frequent as Disney busses, so we ended up walking back to the Doubletree.
(at DD, you could be waiting for a while for a bus to come)
So pretty much, the transportation is ok, its usually gets you where you want to go, but if you have a priority seating, then just make sure that you leave plenty of time to get there.