Pity that they don't open source it. I've gone through multiple image editors on Linux, and none of them have the simplicity of Paint. The layout and functionality is incredibly intuitive. You drop someone into Paint, and even if they've never seen it before, they can start doing stuff within a minute or so. You drop the same person into GIMP, and five minutes later they're still trying to figure out how the hell to…
Pinta has always been my simple go to image editor on linux. Similar to Paint.NET
But 1.7 fixes this issue. It's a development version and not considered "stable" yet (though I haven't experienced any issues so far).