I’ve often wondered, if it would be possible to keep one hand on the mouse and just use a single hand for typing. This would especially speed up pointing-intensive tasks such as editing graphics. Matias actually sells a keyboard called the “Half Keyboard” that allows one to do so. As the name implies, it is half a keyboard with the mapping of the left hand that allows you to switch to the right hand mapping via Shift. You still type with your left hand, but can use the muscle memory of your right hand. This post has details on how well this works:
Unlike many purported "solutions" to typing problems, Half-QWERTY has actually been tested – at the University of Toronto Input Research Group (with which Matias is affiliated). After about ten hours of practice, most test subjects were typing with one hand at over 50% of their two-handed typing speeds; one subject hit 88% of her two-handed rate. Errors, however, were about twice as frequent as in two-handed typing.
The post also mentions a few caveats, notably the problem that if you do not already touch type, usage might be a bit difficult to pick up. For touch-typists it would obviously make a great keyboard for mobile devices.