Sorry if this has already been posted... did a search... read all the stickies... LOL!
I think it would be more realistic to add enviromental effects on movement. In other words:
Swamps and mud are squishy. You would walk slower in swamps and fall down more if you tried to run (because they are sooo slippery), but there would be far less damage (hence, squishy).
Snow is ideal to walk in, so long as it\'s shallow show. Deep snow means you sink in, and, depending on the depth, slows you down tremendously, as well as dramatically lowering physical stamina.
Rocky areas are loose, but hard and sharp. While you could run/walk faster in such areas, where there is a lot of \'rubble\' (e.g. gravel and small rocks) you fall more often when you run, and sometimes when you walk. But where there is no rubble, you shouldn\'t fall down much.
Paths are smooth, and rough. Don\'t fall down much, and don\'t take TOO much fall damage (except stairs)
Sand is hard to walk through, because it is hard when you step, but sinks when you take the next step. So it should wear you out fast, reducing physical stamina, etc.
Also, running down forest paths if you run over a sizable root you should trip and get a faceful of dirt. But the woods are easy on the feet, so physical stamina should decrease slowly.
Dungeons are dark, dreary and unnerving. Mental stamina should decrease while in such areas, and taking damage in sewer/dungeon water should poison you, since who knows what bacteria live in the sludge.
I hope these are good ideas.