The chorded keyboard is not as efficient as two handed QWERTY. Englebart reported getting 35 words per minute with his right hand and 25 WPM on the left after extensive training.
Granted, this is a good speed for having one hand free to use another type of input (pen, mouse, touch screen or whatever).
A chorded keyboard is also a promising idea for mobile computing where a dedicated physical qwerty keyboard is unwieldy.
I wasn't able to see enough of a benefit to try building one or purchasing some of the existing products. At the right price point, I definitely would try it as a novelty.
It seems there is a chicken and egg problem of inputs and software that makes you efficient using them.
Of course, if you wanted to do programming on a chorded keyboard the chords you need are totally different, but apparently it's still very doable: http://plover.stenoknight.com/2010/04/writing-and-coding-wit...
On the other hand, I believe there's lots of room for improving on the status quo in a way that isn't necessarily intended to ever supplant the conventional alternatives, just focusing on some subset of users who have a good reason to be willing to invest a little more time in becoming more effective. (This is part of the process that led me to design my own custom keyboard.) If you look at Emacs or Vim users, it's clear that some people are willing to spend a lot of time learning skills that improve their efficiency.