Productivity hit and frustration, I would say. Motor learning is hard, since it takes a lot of repetitions. Motor re-learning is arguably much harder, since you

Productivity hit and frustration, I would say. Motor learning is hard, since it takes a lot of repetitions. Motor re-learning is arguably much harder, since you have an interference of learned and new patterns. Keyboard familiarity is also heavily depending on motor learning - distance between keys, their position, height and so on. So you just have more to learn at the same time. I also have another warning, based on my experience: it is for many people difficult to keep proficiency in QWERTY after they completely switch to Colemak or Dvorak. It is hard to describe: like you've been touch-typing on QWERTY for 18 years, and you know where the keys are, because if you look down, you immediately find them... but something is blocking you from finding them while typing. If you switch completely at work, find a week or two without much stress. New layout can be infuriating enough :)