Hello Paint.NETers!
I don't browse the forums at all but I am a Paint.NET user and while reading a community spotlight on creators.xna.com I noticed one of the tools the developers had used was Paint.NET!
Original article here.
Go through the questions and once you reach "What other tools/programs do you use to help you make your games?" you will find amazingness.
Edit by Rick: Looks like the link got lost somehow, so I fixed it using your first post.