You guys are getting whipped up into some pseudo-psychological storm about poop trolls, so let us discuss the finer arts of dealing with Dwarven wastes that we so crave. The mere existence of it would generate jobs, you could place a toilet above the jail, you could craft toys and shields from it, you could even spread it as a fertilizer upon your crops. I'm sure there could be money to generate from the mushrooms that would sprout from feces, and you could even create drugs such as Jenkem from it.
EDIT: Another use could be a weapon! Throw it with a catapult at goblin hordes!
See? What are you people so worked up about? The trolls are becoming more subtle and tame, already!
Anyway, assuming improved farming comes down the tubes, a sort of "sewage treatment plant" was what I was hoping for, anyway... Basically, a fungus and worm farm that turns the sewage back into valuable fertilizer for the fields, which, in turn, would require refertilization, lest the soil become depleted. (*ahem* It's a crappy job, but someone has to do it.)
It would also help move the game towards a "Conservation of Matter" goal I would really like to see implimented. The game, as it stands, creates matter from farms, and annihalates matter once eaten. (This is carried over with how recycling metal works, and other problems, but that's a major one I'd like to see addressed first.) Hopefully, we could start working DF towards being a model self-contianed ecosystem, with the same matter sticking around, being perpetually re-used, especially when we get the new army and caravan arcs that will put finite caps on the amount of trade material or goblinite flooding the fortress...