I've just shot two rolls of 100ASA b/w film, one in a Kodak Retina 1a and the other in a FED I. Using 'Sunny somewhere between f8 and f11' and extrapolating backwards accordingly, I was pleased (and surprised!) to find that I didn't have a single unprintable exposure amongst the 40-odd shots. It has to be said that some of the content was inevitably rubbish, but it was all reasonably well exposed rubbish. Part of this undoubtedly comes down to the Sunny rule, but as light levels fall guesstimation becomes more difficult and I believe that past experience plays a greater part. Using mainly a totally manual TTL metering camera and taking note of the indicated readings over the years in various lighting conditions undoubtedly helps when one is meter-less.