Hi,
I wrote a sudoku software for Pocket PC. It's not a killer app, but it's quite useful for more advanced techniques on pocket pc since it's got automatic pencilmarks and a coloring tool.
If you own a pocket pc and want a powerful sudoku software, check it out.
I also plan porting it to the PC platform, but for now, it's just a Pocket PC app.
http:\\www.magic-sudoku.com