One problem related to speed control springs has been reported for the 2010 Toyota Prius. The most recently reported issues are listed below.
While driving my wife's 2010 Toyota Prius from colorado springs to alamosa we experienced the following anomaly. We were on the freeway (I-25) driving south on level terrain with the cruise control set at ~70mph. I noticed a significant increase in the engine rpm and could see the engine display for the engine in the pwr mode. I disengaged the cruise control and waited a short period of time and reengaged the cruise control. A short time later (~15 minutes) the rpm increase occurred again and I once again disengaged the cruise control. I did not use the cruise control again on the trip. My wife has used the cruise control rarely since her use does not include freeway driving.