We (almost!) always stay at CBR, and although we always have a car, we almost never use it when staying on site (and never use it to do Disney things!).
Our last vacation to WDW was in December 2003 - we used the bus to get to each Park, would hop back and forth between MK and EPCOT on the monorail, with no difficulty could transfer to a bus heading to MGM from the Transportation Centre, for example. Disney busses can take you back and forth to Downtown Disney, with virtually no wait either coming or going.
We did the Early Entries via bus transportation with no problems (other than trying to drag our lazy bones out of bed), and when we decided to eat at Trail's End, Fort Wilderness, we left the MK, and hopped on a boat which took us FW, after a quick stop to unload and load guests at the WL.
While we didn't do any waterparks during this last vacation, we have on other occasions, and used Disney transportation to get back and forth with no problems.
During all of our past
Disney vacations at CBR, and also at PO-R, and the All-Stars, we have never had any problems with Disney transportation, other than sometimes a crowded "ride" home at the end of the day, from a Park (which could be avoided if we sat down and had an ice cream somewhere, til the worst of the crowds cleared).
If our vacation at WDW is for more than 5-6 days, then we might take a day off from the parks and go shopping at one of Orlando's malls, or perhaps go off property to eat...but that is the only time we'd use a car.
