How thick is a wall of force? If it is infinitesimally thin, it would presumably function as if infinitely sharp such that falling on it could have interesting effects.
(Would an object stay together [in a physical sense electromagnetic forces pass through the wall, so molecules would presumably not be severed by the thermal momentum; electrical signals of the nervous system would presumably also pass through the wall--unless the wall happened to pass through a synapse where chemical communication is used]? This would allow one to step on wall of force with little harm, temporarily cutting off blood circulation. A separation above the diaphragm would severely limit breathing and the wall would block circulation. After falling onto a wall of force getting up might be quite difficult.)
While the rules say that formation of the wall will fail if it intersects any substantial object (obviously this excludes air), if the wall is infinitesimally thin, it is implausible that the wall would be disrupted by any object falling on it (such would make dispelling as simple as chipping off a bit of ceiling above the wall in a common use or a similar action for the bottom or a side of the wall).
If the wall is on the order of a millimeter thick, it might still be unpleasant to fall on to it. If the wall is somewhat thicker, it might be used as a kind of tightrope (even if frictionless, one could still straddle the wall and "jump" across).
Is surface of the wall frictionless (i.e., the "force" is perfectly perpendicular to the plane, analogous to an air hockey table)? (This is less important for the standard [necessarily vertical] wall of force--though it would make climbing or rappelling interesting--, but horizontal or inclined variants would have interesting uses if frictionless.)
(I do realize that applying our world's physics to a magical environment is problematic.)
If a specific version is necessary, assume 3.5. (The rules-as-written tag was used to exclude house-rules variants, not GM interpretation of under-specified rules. Perhaps the cultures of the various editions are sufficiently different that even with similar spell specifications the common [within each culture] interpretations would differ. If any version provides a more specific understanding of the spell, feel free to use that version.)
As an example, what would happen if a rope with a grappling hook was tossed over a wall of force and an attempt was made to climb the wall?
(Even though for most uses, a wall of force would be surrounded on sides, bottom, and top by other barriers [e.g., when placed wall-to-wall, floor-to-ceiling in a corridor or room] so behavior of the edge would be less significant, I assume that this issue has been encountered in game play by now.)