I've found that my typing performance (speed, accuracy, flow) are noticeably improved if I am swaying slightly, mostly side to side, in a non-regular manner. I would estimate that the overall movement side to side is less than an inch.
This occurs for all typing tasks, and surprisingly also affects my piano-playing performance. It is not necessary to be listening to music (though it can help), and only sometimes does the movement correspond to the actual typing itself. I also find that if mistakes are made, this movement is disrupted, and that consciously re-starting the movement helps restore the induced state.
What could account for this effect?
I would personally suspect that it's acts to induce a sort of 'flow' state, but I'd like to know if this has been studied or even noticed elsewhere...