active/active just means both uints handle SOME of the VS's at the same time. If one fails, then both units handle ALL the traffic. Some people don't like this... But I do.
Most objections come in around the argument that in a failure situation a single box may not be able to handle then whole peak load. But that's doubly true of running it all on a single box in the first place :) In a situation where you don't have a failure, you do have more capacity.