@makkau - "unfair play" isn't a good option, cause that could be interpreted all sorts of ways. You know, like beating someone is "unfair." (It'll happen.)
@DrKarotte - Don't like the idea of a sort of "auto" green thumb being given. If it's a "standard setting," then people who don't notice it won't realize they are giving a green thumb. While it's nicer if they do, it should still be up to them or it stops having any meaning. Perhaps a suggestion of giving green thumbs would be good. I wouldn't want something popping up in my face all the time about it, but perhaps have that notice pop up to a new player's first five games or some such, until they get the idea the site would like them to do this. The FAQs talk about it, but no one reads those things.
@ringersoll - I think you are more anal than me.

I do give green thumbs to nearly everyone I play, unless there's a reason I wasn't particularly happy but not worth a red thumb. I've given red ones, but it's not common. And I do leave a note on everyone I play.

I just don't go as far as you, mentioning what games we played, etc. Usually it's something simple like "Kept up with turns fine" and sometimes I'll add something special, like if they were badly losing and were courteous enough to see the game through. And of course, I make a note about anything bad.
Of course, it's all probably a moot point since we've gone way off topic.