In regular (2008 SQL Cluster) MS SQL Cluster, as an example we had 3 nodes, but two instances on two nodes separately, and third node was empty (no instances) and ready to take a failed instance, as needed. (the nodes did not need a distinct SQL instance)
but in the new Always on featured 2012 version, it seems like you need an instance on all 3 nodes, other than the cluster instance. (so 4 sql instances instead of one, previously)
Does that not imply 3 times the resource?