I wasn't sure about posting this here, as I'm fairly certain most of you are already familiar with the subject matter.
It occurred to me though that many of you likely know more than I do about it, and as such could possibly either correct any of my mistakes, or add some other cool things I might have missed...
I basically revisited the Resynthesizer plugin with the Heal Selection script for filling in selections on an image based on surrounding textures. I really am amazed at some of the results that the plugin manages to produce (especially on random nearby textures like grass/sand, and skies).
I know things tend to break down on boundaries, but depending on the orientation, and the sequence you heal selections, many of those limitations can be overcome quite easily, I think.
Anyway, if you have a few minutes and wanted to check it out:Getting Around in GIMP - Heal Selection (Resynthesizer)