Have you seen this video? I think this robotic arm is mocking Timo Boll. And I guess this is ping pong, not tennis, but now I really want to watch a robot compete in a tennis match. Its all I've been thinking about, all day.
Did he cheat at the end? I don't know the rules of ping pong, but that's my hypothesis.
It'd be interesting to see an actual match when the robot has a learning system built in. And by "interesting" I mean "amazing, someone do it now."