Growing up we used to have a chuck roast every Sunday, but I had never heard of flank steak til I got married and was introduced to my mother-in-law's 24 hour marinade. Then my father-in-law would grill it to brown on the outside and about medium (right, LG?) on the inside. Incredible.
Actually he would leave it med rare on the inside. Mind you, not rare enough for me but hey, he tried.