Ask HN: How did you keep improving your typing speed after 100 WPM?

I type at 100+ WPM on a Laptop (Qwerty) keyboard (120+ on a nice cherry blue keyboard). I know many typists get faster than this. I practice on http://play.typeracer.com/ a bit, but it doesn't seem to improve my speed much.

I have no need to type faster than 100 words per minute, but I'm interested in how one would keep improving when all the learning resources are targeted at beginners.