I think the biggest problem with adoption is going to be integrating them into traffic. A car that obeys the speed limits and follows at a safe distance is going to have issues driving in someplace like Los Angeles. It will be interesting to see how that plays out. For instance, what happens when other more agressive drivers learn that they can just cut off driverless cars and the software will just happily slow down to let them pass? It's a really interesting problem set.