Answer me these questions three!
No, but seriously. I've seen reference to this problem cropping up before, but never quite to the extent I have presently encountered. What happened was this: I had a dwarf throw a tantrum and destroy my cave river bridge. Pursuant to a long-standing plan, I have built everything of relevance on the far side of the cave river, including my stone supplies, all my food, and my well. Almost immediately after the bridge was destroyed, I suffered a frogman attack. While my crossbowman on the surface-side did banner work, what really killed them was the large serrated bronze disk trap just inside my first room (where the well is.)
Now, however, my fortress is almost completely paralyzed. I (foolishly) attempted to place a new, larger bridge where the old one was; realizing that the stone involved might be on both sides of the river (somehow, despite my stone stores being on the deep side), I then attempted to install a smaller bridge crafted of moonstone off to one side. I've never used moonstone for anything, so it should all be in my stone stores, and I have guys tasked to build it on the side where the stone is. No problem there.
However, not only do the dwarves refuse to build either of the two bridges, they refuse to do anything else. An increasing number want to drink, but they refuse to even enter the room where the well is. There's a farmer standing in the doorway who won't take the one step to get there. Granted, it's pretty bloody at the moment, but that doesn't seem to be worth dying for. (Not that they will enter the room to clean it up, either. ) The guys topside, of course, are starving to death because they can't get to the food stores. I've got saves of all of this; saving and reloading doesn't appear to have changed anything.
That problem aside, the game is everything I'd hoped for and more. Good on ya, Toady. I'll kick you some bucks as soon as I'm, you know, gainfully employed.