The Coding Horror article actual got me thinking about this as well.
Generally, I large classes I will put a region around the member variables, constants, and properties to reduce the amount of text I have to scroll through and leave everything else outside of a region. On forms I will generally group things into "member variables, constants, and properties", form functions, and event handlers. Once again, this is more so I don't have to scroll through a lot of text when I just want to review some event handlers.