The Janko (or Uniform, or Chromatic) keyboard is simply, in our humble opinion, an intelligently (that is if your intelligence includes music theory) designed piano. You can find out lots about it here in Wikipedia.
The world's leading expert on, and player of the Janko keyboard is Paul Vandervoort, his website is well worth visiting to see the examples of how a Janko is played. One can readily see that it is a faster, more natural way to play a keyboard.
For an excellent review of how cool a Janko is, see his video: http://youtu.be/cK4REjqGc9w
Paul has nearly completed his prototype keyboards, using a unique and quite innovative key design with an excellent action and other innovations, as posted at http://www.daskin.com/. We'll try to keep you and this page updated on the status of this endeavor. Update: See this video of the working prototype.
Another definitive website we've found on the subject is http://squeezehead.com/uniform-keyboard/.
Roy Pertchik has come up with the interesting idea of coloring the keys with a three color combination. On his two row Janko layout it is surprisingly useful, as the colors give one a huge amount of information about how the notes fit together in a harmonic lattice. Music Theory made visible, as it were.
He has been asked to illustrate his ideas and put them here. For now, here are links to his paper and a video he made