I got into those a few months ago, when I started my new job. A bunch of us in my department are addicted to them. We enjoy the 'evil' puzzles on that website! I thought I was good at them, but one of my coworkers is a freak!
Haha, I warned you they were addictive. I got a book of 200 of the hardest puzzles for X-mas. Includes 10 Megasudokus that have 25x25 grids, rather than the 9x9. They're beastly. I think I'll stick to the 9x9's to the point where I can rock them in 10 minutes (I'm exaggerating here). Then I'll try to tackle the Megasudoku.