This video isn't really exciting, but it does show that hydrofoils can work in windsurfing. I've been wondering about that for a while. It also shows that adding a hydrofoil is a bit pointless.
The board doesn't seem to be going any faster with the foil (watch for the traditional board in the background). I expect this is because the foil requires a lot of drag to create the necessary lift. The foil does make the ride smoother, but that seems boring. Maybe the foil would come in handy in wave sailing?