> I would worry that with no physical presence on the keyboard, I would spend a lot more time looking at the keyboard figuring out where the function key I need is than actually getting things done.

Exactly. In Eclipse, F5 steps into a function call, F6 steps over it, F7 returns from the current function, and F8 resumes execution, and mistakenly pressing the adjacent key can be frustrating (although, with time-travel debuggers, this issue might be alleviated?).