Well, Personally I think that not only is a 12 hour duty limitation invaluable, but is entirely feasible. I just did a quick examination of our lines this month, and out of the entire month only 1 pairing on 1 day was scheduled longer than 12 hours (excluding a few ready reserve schedules and stand-ups). This, by the way, is at Colgan (yes, COLGAN!) out of EWR. In fact, most of our scheduled days are less than 10 hours. If Colgan can do this, than I think others can as well. This would also have the added benefit of reducing stand-ups across the board.
I understand that this is only scheduled time, but if we can build lines to about 10 hours, extendable to say 12 or 14, it would greatly reduce the amount of fatigue from long days.