I posted a comment to the Paint.Net forum a couple of months ago. I have just checked the latest beta (v2.2 Alpa 1) and they have added in my suggestion.
I can't find the forum link anymore, but the suggestion was that when using the selection tool, clicking the right button at the same time as the left button would move the selection rectangle rather than resizing it from its origin point. Previously it was annoying to use if you didn't get the origin point exactly right the first time.
It is great when people implement your suggestions. Thanks guys.