Being able to give a list of weaknesses in something like git, a sensible discussions of the pro/cons of the approach taken by git, a comparison with the behaviors of other systems (with their pros and cons) and some idea for potentially improving it.
With the ubiquity of DVCSes and Github etc, I don't think there is an uber-hardcore level in source control. "Has used git etc in a team setting" is the closest I can find.
