One problem related to anti-lock brakes fail has been reported for the 2008 Toyota Prius. The most recently reported issues are listed below.
The car's anti-lock brakes fail to engage when the traction control kicks in. Thus, the car slides forward uncontrollably. I have avoided accidents only by swerving. Additionally, the traction control will activate when on dry pavement. Thus, normal stopping can be difficult if the car's traction control is activated (typically due to a bump/pothole).