Do the OldGuy's coastline tutorial if you can. It's for GIMP. It's, like, 8 steps and it works a treat. It's quite possibly the best coastline tutorial I've used since it gives lakes and islands and things like that as well.
That is really lovely, too. I don't know that I could ever see those forests as satellitish. They're too blurry for one, and those mountains are a little... well, the one in the middle of the bottom half looks like a spine. They're a bit too dark, I think. They still look like they're on top of the landscape, not a part of it. That's just my five cents, though.