hey
how can you make an object follow the geometry of a terrain?
I looked at the floor constraint but that one is only a flat plane.
Think about a bike riding over a ground and you want the wheel
adjust automatically.
Hmm…
A “follow Path” constraint to a curve.
Curve with “shrinkwrap” modifier.
Would that work?
Sorry if it doesn’t… Just thinking out aloud 
[Edit: Just read the last part again. Reply seems even more doubtful now]
I think you’re on the right track makr. I’d retopo a curve to the ground.
If you want the bike or whatever it is that’s following the path to come off the ground at any point, you could just keyframe the influence of the follow path constraint.
Here is an alternate method using scripting in the game engine http://blenderartists.org/forum/showthread.php?t=130591, not that I understand it myself but it came to mind when I read the question
If the object is a vehicle, you might want to consider ROUBAL’S work.
http://blenderartists.org/forum/showthread.php?t=164134
It is basically a setup scene with the curve already shrunk wrapped to the terrain.
Ah I see
so we are back to the curve wrap. I was curious if there would be something new
like a real time collision detection for geometry instead of only a plane.
SketchUp Physics can do that as well quite nice.