One problem related to speed control cable has been reported for the 2008 Toyota Prius. The most recently reported issues are listed below.
My mother has a 2008 Toyota Prius and was pulling into my driveway. The approach to the driveway is uphill and the driveway is more of a parking area with an access apron. For some unknown reason, the car's engine revved (very high rpms - I could hear it from the basement). The car grazed the side of the house, went through a short wall (brick - about 1 foot tall, 1 foot thick and 5 feet long) and an iron deck gate. The car ended up on the deck after breaking off two 6x6 support posts. The deck has horizontal stainless steel cables instead of pickets, and I believe that these are what kept the car from going over the edge - a 25 foot drop.