I flew IAD-SJU RT a couple weeks ago and both overwater legs I lost access on the ViaSat. Connected to wifi, of course, but no traffic passed. The coverage map seems to indicate overwater in the Caribbean, but I couldnt access any web sites at all until we got close to land...
I actually sat next to guy on a flight last month who is leading the ViaSat effort. He says this is just the begining, and they are working hard to deploy the hardware...