I've been running around with the 0s cd RC for a while now.
I've got some mixed feelings about it, but for the moment I'll stick with it..
Call To Greatness and Song of Aid doesn't give you much more of a RC spam than it would with 6s cd, since those skills only give you defeat events every 5 seconds.
But there is places where the 0s cd is absolutely epic. Did Battle of the Deep-way skirm with a champ-heavy group, and my HPS was at 4-6k, on some groups up to 8k, no healers needed there.
The first groups in SG is also a place where I'd recommend it, if you can just get the crits off and/or have a mini give you CtG, it helps alot in keeping the group alive until the corruptions are removed.
Haven't tried BfE T2 with reinforcements yet, but I believe that's another place where a 0s cd will be very useful.