In a recent New York Times article, John Markoff tells of how he used his Garmin GPS devise on his bike to reconstruct his bicycle accident.  As bicycle accident lawyers, we have had several cases where our client either had a GPS devise on their bike or an app on their phone that tracked their route just prior to an accident.  In each of the cases, the GPS data was helpful in corroborating our clients side of the case.  Overall, I believe that GPS devices or apps are helpful to bicycle cases.  Especially in cases where the at-fault driver tells a very different version of the accident, the GPS data could potentially win the case.