One of the things I love about Disney is not having to get in a car for a week. I personally think that Disney transportation is very good from most resorts (Fort Wilderness being the big exception), and don't mind waiting a little while for a bus every now and again. Of course, I take public transportation in Boston on a daily basis, so I'm used to waiting.
That being said, if you plan on going to several resorts, it's not always going to be easy to go from one resort to another. It will be easy to get to the Floridian and the Contemporary, but if you want to go to the AKL, one of the moderates, of the Epcot area resorts, it's going to take you a little longer. It will depend on what time of day you are going. It's more difficult getting to another resort when the major parks are closed.
When I go to another resort, I usually cab it one way, and use Disney transportation the other way. For example, if I'm going to a character breakfast, I'll take a cab to the resort, and then use Disney transportation to get to the park I plan on spending the day in. If I go to the Boardwalk in the evening, I'll take Disney transportation to get there, and hop in a cab to go back to my resort. Even cabbing it both ways could be more economical then renting a car.
I did an Illuminations cruise in December. We planned to spend that day at Epcot so we could take the boat to the Yacht Club from the International Gateway and we wound up taking a cab back to the POFQ. Our driver offered to let us off at the International Gateway so we could walk through Epcot and get a bus, but we decided to take a cab because we had a very tired six year old with us. It only cost about $10.
I am also staying at the Polynesian in August (the 13 through the 20). Can't wait!
Karen