I was thinking of Ambidexterity in terms of Diablo 2. You swing twice, once with each hand. The weapons act with the worse Recuperation Time (eg. Using a fast sword and and slow axe, they would both have the Recuperation Time of the axe.) One of the swings happens in between the others. So timing wise, it's a bit like:
One weapon: Swing, wait, swing, wait, swing, wait...
Two weapons: Left, right, left, right, left, right...
Simply by weilding a second weapon, which anyone strong enough can do, you get twice as many attacks in the same Recuperation Time, but without training you're so uncoordinated that you can't hit anything. Your Offence is never improved by this skill, only your Recuperation Time. Your Offence is penalised without training.
Character Level or Attribute restrictions would definately be required for this skill, as with any other.
