Brain-controlled user interfaces are an important wave of the future. I think their most essential application is in making it possible for the physically disabled to interact with the world, but by no means do I think we should stop there.
To this end, I'd like to mention the OpenBCI initiative. They aim to create an open platform for brain-based computing interfaces. They are using Arduino as the basis for the system. So for about $500 you can get a brain-reading board. If this sort of thing is of interest to you I highly recommend checking it out.
Personally, I'd love to try this out as a means of remotely controlling and training a robot.