(via Daring Fireball) Tog from several years ago on mousing being faster than keyboarding, but subjects saying otherwise. (Like Gruber, I remember reading this years ago, but it’s great to find/refind the article.)
I wonder, though, if the subjects were saying something else. Perceived speed is not entirely made up of real speed, but also the distraction factor. So maybe the subjects were really saying that keyboarding is a less significant mental interruption, because it’s easier to mentally shift states (and shift back after). It could be that even if the shift is faster with a mouse, it cramps the thought process more than the keyboard. Perhaps the time back to task is shorter, but the efficiency is down for longer.
I have no idea how you’d measure this, though.