One problem related to transmission gear slipping has been reported for the 2008 Toyota Prius. The most recently reported issues are listed below.
Automatic transmission slips into neutral unexpectedly, and when it does, often you can't get it out of neutral without turning car off. This has an electronic shift selector. This appears to be a rampant problem with this car. Do an internet search on 2008 Prius slips into neutral and you will see many people are having this issue. Very dangerous when this happens on the highway.