My fortress is humming along and entering it's 7th year. Population is 201, and the King is on his way. Sieges regularly get made into hamburger in the Gorge of Death, and two dragons have come a-calling. All in all I'm pretty happy with the way things have gone.
Last night I had my first brush with a player-induced misadventure.
I figured out via the stocks menu that I had an underground river/pool, so I carefully prepared an entrance, and breached it. Eureka! An underground river! I stationed Kosoth the Mace Lord at the breach point to handle any water critters that got frisky and began planning what to do with the area. Kosoth promptly went into a battle trance, and chased the critters into the water. Note that he couldn't swim, and there was no shoreline, so he began drowning while fighting them. He killed FOURTEEN of them before he drowned. As a hero of the Duchy I couldn't just leave his corpse down there, so began building pumps to pump it out.
The pumps quickly overwhelmed the ability of the river to carry away the water, and I realized I was in trouble when the lever to shut the pumps off showed as being under 7/7 water. I quickly cut a drain for those tunnels into the Chasm (yay Chasms!) and walled up the tunnels to prevent flooding all of the delvings below the river (which are a lot, but not the industrial area, thank goodness.) That was a near thing, and we almost had some kids walled onto the wrong side of the tunnels.
Now I was left with the problem of shutting off the bloody pumps. The lever was underwater. I decided to drop a 1 square block of ceiling on the power transfer gear. Amazingly enough that worked perfectly and the waters have receded. Now I just have to route a better drain for the pumps and maybe I can get Kosoth's body and gear out. :-)