I've been psyched about the Emotiv EPOC and the NeuroSky MindSet for a while, even though I've never seen them in action. Now I have: Tan Le gives a demo at TED. She shows how you can easily use your brain to make a cube move around the screen.
Cool, sure. But I feel like she, along with a majority of the Brain-Computer Interfaces world, is missing the point by saying "you can use your brain to control the computer." You can also use the computer to read your brain!
Beer van Geer gets this. His program, Dagaz, is a game that you win by concentrating. Naturally, you'll get better at concentrating as you get better at the game. It's like flipping the input/output around: you can use a keyboard to enter data to your computer, or you can play TypeRacer on your computer to get better at typing. The difference is that getting better at typing only helps you while you're typing, but getting better at focusing your brain helps you all the time!
Someone in the audience pointed out "could you use this to help you have better (more productive, happier) work days?" Yes! Yes, you could! And that's only the beginning!