Really? What event would you use to mark the start of private space exploration?
This is the beginning but nothing is certain at the moment. I wish SpaceX only success though, they are working on something great.
If they fail they will point at this mission as an example of a foolish pursuit that should have been left in the hands of government agencies.
Either way this is, without a doubt, the start of the private sector launching into space exploration. Nobody can point to any other private mission that launched a capsule, docked at the space station and then returned cargo to earth.
put in other terms:
$ git commit -a -m 'Here we go!'