Which arrangement of “Submit” and “Cancel” is most effective?
Thanks to a great usability and eye tracking study by Luke Wroblewski & Etre, we now know.
The answer, surprisingly, is that layout B was the most efficient. Users located and clicked the Submit button fastest on layout B.
But users also were concerned that layout B, if used on a long Web form, made it too easy to accidentally cancel the form. With that factor considered, layout A became the favorite, because it presented a good mix of effectiveness and efficiency.
Seems right to me. You can read the full study here.