I'm not a fan of Morton's of Chicago restaurant (ripoff prices) but today's newspaper had an interview with their chef who explains how to properly assess doneness of steak.
"Just touch the steak to see if it's cooked. If you want it rare, it should feel like the hardness of the knob of flesh below your thumb when you make the tips of thumb and forefinger touch. Touch your thumb with the middle finger if you want medium; fourth finger fore medium-well; and pinkie for well-done. This method has always been used in the steakhouse industry and it hasn't failed me yet."
He explains to cook a steak properly at home, use a cut at least 3cm (1.2inch) thick. Heat skillet with oil until smoking hot. Sear on one side for three minutes, covered in a dome-shaped lid to allow steam to circulate, then cook other side to required doneness.
(I must say three minutes on the first side sounds like a lot. I like my steaks quite rare and i don't think I ever cook them steaks that long) I'll measure next time.
He advised that ribeye is the best, most flavorful cut. I enthusiastically agree.