Crap software, but free. No autosave, computer freeze with wrong picture copy. ctrl+c without selection copy all frame in clipboard and crash my computer if a picture is too big. Why you don't block ctrl+c inside paint without selection?
The program itself is legit, but beware of the site. Deceptive "Start Download" buttons could easily fool user into downloading spyware, not Paint.net, onto hard drive. And once those nasty programs are on there, plan on doing a system restore to get rid of every last speck of them. I'd download this from CNET instead.
Good photo-editing software, and good for quickly making good wallpapers such as planets, etc. Sometimes able to do simple photo manipulations, but somewhat bad at image authoring (for example: drawing illustrations of clipart)
Recently switched to the GIMP, which is more advanced and great at advanced things. I still use Paint.NET sometimes for simple things, which is easier and faster to do in PDN than in the GIMP.
I recommend Paint.NET to beginners or people who need a bit more advanced program than MS Paint. When you have used Paint.NET for a while, then switch to the GIMP, or/then to Photoshop, which is more advanced.