Incidentally, people always say they hate text written in capitals "because it's like shouting." I hate it, too: not because of anything to do with shouting, but because it actually makes it harder to read the text.
With a mix of upper and lower case, there are visual clues to help your brain recognize the word before you've actually read it.
Take the word elephant, for example. Some of the letters are taller, and some (the p) actually hang down lower. Even without reading it, the word has a shape that gives your brain a visual clue as to what you're about to read.
Now, if you write it all in capitals, those clues are missing, as every letter is basically the same general shape and height: ELEPHANT vs. elephant.
Sort of like the font question, IMO. Details matter.
