First off I am a real fan of the WDW transportation system, I think it is awesome!
I am a terrible driver, so I do not drive at WDW, when DH is with me, he will drive. Therefore, I almost always take the bus, monorail, boat, etc.
I have found that the transportation system overall is efficent and well run. That being said, I have experienced transportation meltdowns.
The biggest meltdown I experienced was at MGM on an extra magic night, it was raining and they cancelled Fantasmic. People were leaving in droves. The line for the All Star buses was back to the security check point! For those who are not familar with the bus stops, All Stars is all the way at the end. My mom and I took one look at the line and one look at each other, and said simutaneously "TAXI".
I have used a cab maybe 4 or 5 times, ( to get to an early ADR or to go from resort to resort, or to go from DTD to a park) and it has always been worth it.
Problem is now, DD never wants to wait for the bus. If there is a line, she ALWAYS asks, "Mom can't we take a cab?". I've created a monster!!!!!!!!!!!