SuDoKu's should be symmetrical; plus reiteration of other comments...
I was going to mention that I just noticed that the puzzles do not have a symmetrical distribution of pre-filled-in squares; which was, I thought, something that was common to all "SuDoKu" puzzles, and differentiates them from more general "Number Place" puzzles, which have the same requirement of having rows, columns, and subgrids having only one number from 1-9 (I've read it was something added by the Japanese) -- this is true of other sudokus in books I have, and those in the newspaper.
I also just noticed there's more than one solution to a hard puzzle I just finished. I see that this has already been brought up, and I don't mean to complain, just to give feedback.