I had thought of writing a Sudoku solving program while in India last year, but then my laptop died on a sudden surge of voltage (not uncommon in India) and I had to shelf the idea. Once back to US, I never found enough time to code the solution and the whole thing just faded away from my memory.
So when I came across Peter Norvig's Python program to solve every Sudoku last week, I took the time to understand the underlying data-structure and the algorithm and couldn't help but appreciate the beauty of the solution (and Python code). I even downloaded the code and tried it out on a couple of puzzles. It worked fast and without any flaw, but with a minor annoyance -- the program must be run as a command line tool and the input must be entered as a string of 81 characters. Not a problem for me, but perhaps not very "user friendly" to most people on the Internet.