To answer the original question, once. When I dump the wort into the primary, I check to see how close my OG is to what I am aiming for.
I am so slow anymore to rack to a keg, I rarely bother to check the FG. Usually its lower than what I expect it to be. I do like to check the Belgian strains, though, as they seem to be more of a crapshoot where they end at.