If it's only used AFTER a stoppage to determine the legality of the "finishing blow" then I like it. The fight where Johnson was poked in the eye for example. Rule that a no-contest instead of a loss for him.
I don't like the idea of stopping the fight, looking at instant replay, then resuming the fight. It should only be used AFTER a fight to determine if it's a win, no-contest or DQ.
When Diego Sanchez knocked out Joe Riggs a lot of people claimed he hit him with a knee while Riggs was still down. The viewers got to see the replay and saw that Riggs brought his own knee off the ground just in time to make it legal. A ref getting to look at that to back up his call is a good thing.