Guessing exposure is easy, but if I worked on a multi million dollar production, I'd use a meter for safety. I guess most of my exposures too and I'm rarely wrong as long as I'm outside in natural light. Sunny 16 (or more like Sunny 13 around here) is your friend. With inside situations and artifical light (which is often used for filming) on the other hand, I'm off by a stop or two from time to time - enough to ruin slide film anyway.
This guy has my respect for having the confidence of doing it this way and getting it right every time.