Here's another version of an animation over the Grand Canyon to test a few more things.
Added some very crude strata just for a bit of extra detail and ditched the landsat texture.
The main test is an for a river using a image mask (10m resolution over 80km) generated in about an hour in Photoshop... magic wand along the river in landsat image, filled with white, manually patched gaps, masked using the slope map (levels adjusted), dropped onto a black background. A further bit of tidying up in TG2 with a slope restriction and you have a reasonably accurate river winding along the canyon floor. It's not perfect up close, but whizzing past you can't spot most of the problems.
The clouds are also animated a little (this is definitely one thing TG2 does *REALLY* well)
The path follows the canyon at a constant speed, with a gradual drop in altitude to a low point and then a gradual climb.
Detail 0.5, AA 2, no GI, motion blur 1.0 (Before you comment on the motion blur remember that this is only every 4th frame of the total animation). Render time about 5 minutes per frame.
http://www.path.unimelb.edu.au/~bernardk/tgdemo/bb_gc_flyover_low.mov 32Mb
(320x180, 3300'ish frames, 553Mb uncompressed)
Attaching a PDF of some keyframe thumbnails.