Well, I guess it depends on what scale you're looking at.  From higher up, it can just be overland movement, endurance checks for horses, Survival checks for navigating shortcuts.  Closer down, there are movement speeds, run speeds, mounted archery (-4 to shoot on double move, -8 to shoot while running, less with Mounted Archery feat), rough terrain slowing people down (and avoiding it with Survival/Knowledge (geography)/leaping over with the lower of your Ride and the horse's Jump), attempting to trap those behind by cutting/knocking terrain in the way.<br/><br/>I like the example of 4ed skill challenges, where you have to succeed X times before you fail Y times, and you can set a few obvious checks, but the player can suggest other plausible things to do as well.