This is a rather brilliant idea: Iron Sudoku, which is basically a Web 2.0 version of one of the innumerable sudoku websites out there. As you beat each puzzle, you gain points on your account; there is collaborative chatting and a friends system. The grid itself is Javascript, and works *very* well in Firefox. If you like sudoku, I'd highly recommend it.
As for myself, if the owner can make a kakuro version I'd *definitely* be sold…
F L I C K E R I N G / F R A M E 
Thanks for the mention, Inquisitor! I actually thought about doing Iron Kakuro, but never got around to doing it. Maybe in 2007…