Here's my submission to the "thing that solved my RSI but which is purely subjective and may or may not work for you" category:
I used to try to type with my arms/elbows floating -- not resting on anything. This seems to be fairly standard advice. For example, you can see it here: http://ergonomictrends.com/proper-ergonomic-typing-posture-a... I've had various doctors recommend the same thing.
But when I try that, the muscles in my shoulders/back get incredibly inflamed, and tension/pain tends to spread throughout my body, eventually to my hands/wrists.
Eventually I gave up on that, and now my elbows are splayed out and rest on the chair's arm pads. My hands rest on wrist pads, and my keyboard is split about 18" (using a Kinesis Freestyle 2). Basically, my hands/arms are nearly always at rest, and no energy is required to keep them suspended in the air. I also try to avoid "reaching" for the upper rows with my fingers, instead I move my entire arm forward to some extent to hit those keys (which is more a 'push' than a 'lift', because my arm pads have a bit of give in them).
I've had no problems since adopting this setup.