Because I never heard about this Paint.NET, I googled around a bit, and wow, I had no idea there were so many free image manipulation tools out there.

Judging by a limited sample of reviews, Paint.NET seems to be ahead of the curve for portrait touch-ups. RealWorld Paint.COM has filter-layers, a nifty PhotoShop-feature that didn't make it into GIMP yet (and which is the only feature I'm really missing in GIMP). ArtWeaver has great brushes, something I'm sure going to try out. And there are still others.

But all in all, for the kind of photo manipulation we do here, I still think GIMP is the best there is. If you want an easier program, you're also going to have fewer features. And if you want better greenscreening, you're going to have to pay for some PhotoShop magic.