Holy cow, I cannot express how addicted I've become. It started simply enough, with a puzzle on a different site. (It was last week's Lenny Conundrum on neopets.com if anyone frequents it.) I went to a site or two to learn the basics, and once I'd finished the given puzzle I found myself hankering for more. Web sudoku is now a daily visit. My personal best time for easy is 3 minutes 40 seconds, and I need to start doing the medium and hard ones for more of a challenge.
It's just as bad as knitting, you know. You start one, you finish it, you think "Gee, that was neat" and before you know it you've started another! Sort of like hats, which I find to be similarly quick and gratifying.
...It occurs to me that this may be a problem. I saw the link to web sudoku in the preview and went 'ooo, sudoku!' and did another puzzle.