Super 2 only has to do with service time, not effectiveness. Basically it is a comparison of the service time of all the players the year they hit arbitration. Recently it has broken down to guys who have come up before the second week of June are in the running to get to their first year arbitration a year early. The first year or arbitration usually hasn't been too disaterous for teams, it's the third and fourth year that gets expensive if the player turns out to be useful.
For instance, Danny Valencia just missed super two status because, surprise, the Twins waited until June to call him up.