Okay, taking this one directly from the main page. Straight from the mouth of our illustrious leader, toady himself.
"I don't yet see a way to make something like rubble or different sizes of rocks a net positive for the game"
This thread is dedicated to finding those ways.
First off, i have a few of my own. Different sized rocks could be used for different things, for instance, small rocks, that of about the size of one's head or smaller, could be used for crafts, rock traps (or murder holes, if you prefer something a little more medieval), and perhaps be cut into bricks for use in construction.
Gravel is a lot harder, only use i can think of off the top of my head is paving roads, which would be not as good as a cobblestone road, but better than a dirt road. That one is all i've got for now.
Lastly, we'd need a new designation 'quarry stone'. Normal mining would be simply digging a tunnel, and generally get you more gravel and small stones as well as being faster. Quarrying would get you larger rocks more often, suitable for making construction stones, or whatever you felt like, but each individual tile would take longer to quarry into stones. Hopefully this would solve the problem of having SO much loose, worthless stone that you have to resort to quantum garbage dumps to get it managed.
Have at it guys.