I think ranking puzzles as to how difficult they are and awarding higher points for the more difficult puzzles in a good thing, but not based on the average time spent. Those of us who are faster solvers in general, in my case because I have been doing logic problems for years, are going to be skewed with higher scores. The cryptograms site scores based on assigned difficultly (based primarily on the length of the quote) and the time take to solve the puzzle. That, to me, is fair. You get credit for solving a more difficult puzzle, as well as your time playing a factor. Perhaps a difficulty rating could be based on the number of clues, or the number of non-direct clues?