Anyway, grass should grow 1/5th of a block tall. It could be used to hide spiders and conceal traps. Constant trampling of grass would cause it to revert to the normal grass block (the current one). Grass could be 'mowed' by punching it.
I'm all for getting something like the better grass mod put into Minecraft proper. It would add a solid level of realism without detracting from the game in any way, or adding too too much to the processing payload. So long as it had an option to turn off for older computers, it'd be golden.