This past week, I wrote up a pretty detailed guide on porting Winforms applications to run on Mono. I originally planned it for my blog, but decided it needed a more permanent home like the Mono wiki.
So here it is: Winforms Porting Guide.
If you use it and come across things that don't work or could be made clearer, please let me know. And of course if you have suggestions or questions on other things that could use some documentation, I'd love to hear them as well. The comment section on this post is probably the best place for feedback, but you can also send stuff to [monkey *at* jpobst *dot* com].