I remember reading somewhere that the Sunny 16 rule - for an f/16 exposure - means noonday sun. I've used it for a long time and I get fine results on negative film (I haven't shot slides in a long time and when I do it's usually with a camera with a built-in meter). One thing I did when I was first learning photography was carry my light meter, but no camera, and attempt to estimate the exposure and then check it against the meter. This taught me a lot about the variance of light throughout the day and weather conditions.
My mentor, John Scarlata, said that his first trip to New Zealand gave him some exposure difficulties. He had to adjust his exposures down 20% or so to account for the bright light (compared to the Southeastern US especially).