I normally work on the advance sudokus and have escalated this recently as I plan to be offline for a week or so next month. If the site ever comes back up, they will either have to clear the leader boards or freeze their records at the date the site went down.
Meantime I am using
http://www.websudoku.com/ (as recommended by wired). The problem here is that their 'evil' level is somewhere between 'tough' and 'diabolical' on sudoku.org.uk so no real challenge!
If you get any news, please post it ....