For those of you that crossed from Windows to Linux and misses Paint.net there is a great alternative program called Pinta: You can download it off the website or search your distro's repository for it.
also, there are all of these online programmes - http://www.youtube.com/watch?v=VyNnZHo5UJo i still use the ms paint clone - kolourpaint, or lookup a gimp tutorial for more thing complicated i got some scripts somewhere to resize images too
I am one of the "casual users" it spoke of--all I do mainly is crop, resize, and maybe touching up. Gimp has too many features I do not use (and wouldn't know how to, lol) so Pinta fits my needs. It does really remind me of Paint.net which is a favorite Windows app.