Terragen is amazingly good for background skies (to be used in other apps). And it's OK for heightfields, I guess. For the Mac user, it's about as useful as screen doors in a submarine, and as far as renders are concerned, you'd best have no interest in using imported models, as Terragen simply ain't up to it. And I don't think it does volumetrics either. Other than that, it's just peachy, as far as free programs with no future development or support are concerned. It's alot simpler to get a digital camera and Painter or Photoshop for those skies--- no time spent waiting for renderings, either. Maybe wait for a storm or a sunset, though, but that's more fun anyway-- more time to play with Bryce or Vue while you wait. :)