I've taught myself on a Yamaha PSR-175 keyboard. Although it sounds rather horrid, it's sufficient for learning on. In the months I've been playing I have only learned a few pieces, such as Kalmah's "Swamphell", Heavenly's "Miracle" and Fur Elise. I can also play myriads of keyboard "riffs" (for lack of a better word) coming from acts such as Skyfire, Children of Bodom, Norther, and of course Kalmah. Having that said, I would be progressing much faster if I dedicated myself to the instrument. However, I feel I am much more of a guitar player at heart, so piano is likely to remain as a secondary instrument to me for quite a protracted period of time. :P