Hi Klebnor,

I originally started out my 3D experience with Bryce and quickly found that it had a very decent array
of terrain generators, filters and other tools that made it pretty easy to make terrains that fit my models, instead of the other way around. As a bit of SSP I offer this render from my gallery where I used Bryce to generate the terrain for my Carrara  render.
http://www.renderosity.com/mod/gallery/index.php?image_id=1843720&user_id=581189&np&np

  I built the bridge model in Wings, and box modeled a terrain "profile" of the canyon to fit it. I imported
the profile model into Bryce, rendered it from top camera using the altitude render, which gives a greyscale heightmap, and then I imported that into Bryce's terrain editor and "attacked" it with the erosion brush to shape it. All I had to do then was import the new heightmap into Carrara and adjust the dimensions of the resultant terrain a little to fit my bridge. Much simpler to do than it sounds.;)
 
Carrara's terrain editor has some neat tools as well, but is a bit harder to come to terms with, at least for me. I think the two apps strengths compliment each other. 
 
  In Bryce you can animate terrains, making changes with built-in filters, or imported bitmaps and setting keyframes for the geometry changes on the animation timeline.  I have made a few animated
creek, or river greyscale animations which import beautifully into Carrara's displacement channel.
In a ten second animation I'll quite often import 10 different bitmaps, one every second, at 30fps, and Bryce does a pretty nice job of "tweening" from bitmap to bitmap. I still can't figure out how to make it loop yet though, heh heh.