According to this Popular Science article, researchers have figured out how to capture 99% of the energy in a deep ocean wave. Looking further into the technology, I find it is a bit like those old water wheels. And I found a terrific interactive graphic that shows how this mechanism works when used on a tugboat as a propeller.
When I see a 99% capture rate, I get a bit suspicious. Sounds too good. And looked at another way, we are talking about an almost perfect wave dampener. You should be able to set up a wall of these near a coast and protect the land from big ocean waves, even tidal waves if the system is powerful enough.
Mind you, even if you captured all of the was energy in the oceans, according to Saul Griffith, it would still only supply about a fourth or a fifth of humanity's demand. I think wave energy will be viable in a few places, but the bulk of our efforts should go towards making solar cheaper than coal. The supply for solar is more than 5000 times the demand!