Well, as far as power advantages, you can go with more agressive port timing without raising other issues like spring bind and drag in the valve train on a conventional head, so the effieciency of the head will be a constant no matter what kind of crazy port timing you go with.

The downside is that right now, I don't believe they have the capability to handle variable port timing [VTEC, etc...] since they're still going to be crank driven.