We had an Icons session on Monday (I'll post a recap shortly) and we quickly decided to "split the dice".
One other point is that when players have to make a general ability test we were still rolling the positive and negative. Though that worked fine, I thought it was a bit jarring to have the Players roll one die for combat and two dice for general tests. I'm thinking of moving general tests to split dice as well. The GM will then be rolling the 'negative' die in combat and in general tests ('negative' die meaning GM rolls the opposing die and adds the result to the difficulty).
The split dice bring up an interesting element. Since the GM is now rolling all oppositions to the PCs, maybe, just maybe when the GM rolls, his roll will be the 'attack' roll against which the players defense is compared. In other words, outcome switches depending on who is the 'attacker'; the zero no longer
always goes with the hero. The tables turn from giving the heroes the constant advantage to splitting the advantage between the hero and the villain. Not sure how this will play out. Maybe the heroes will become less 'heroic' as they loose that zero goes with the hero advantage. It's a minor thought but it could change the dynamic of the game quite a bit.
Beyond that, we're still a bit stuck on keeping stuns and slams within the flow of the combat. I'm going to re-read the optional rules in the Villainomicon to get some more clarification.
Anyway, the split dice definitely moved the combat forward more quickly.