I started learning how to use Paint.net today and decided to re-design my blog. It was a lot of fun! I still have to make my blog button, but I really like it. It is a lot more versatile than Paint. From what I understand, it's a mini version of Photo Shop. Once you learn the basics of Paint.net, it's fairly user friendly. I was having issues figuring out how to remove the white background from an image. I did a search and after looking at several, I found this very helpful video.
If you decide to try Paint.net, let me know how you like it and if you found any good resources on how to use it.