Problem: Gobbo ambush decloaked in my dining room
Solution: Every single dwarf had mining or woodcutting enabled. Mass draft. Clean up the blood.
OH MAN, that is insanely epic. I demand fluff pieces be written about situations like this post haste.
The most challenging situation I've had to deal with was rather mundane, but fun to work through:
I created a massive pump system in order to supply water to all points of my fortress with, what I believed, was an ingenious plumbing system. When I finally laid down all the pressure plates, levers, floodgates, grates, and constructed floors, I turned the system on.
As you might imagine, there were problems.
Predictably, I ended up flooding my fortress before I realized there was a problem. Before I could turn the switch off, the, in hindsight, poorly placed control room became completely submerged (Protip: never put the majority of the pumping equipment in the control room, no matter how cool it sounds).
So, instead of abandoning the fortress, I gathered all the survivors outside and lived in wooden shacks and impromptu holes in the ground while I started the arduous task of pumping out the water (difficult given how much water was being pumped *in*).
Finally, having accomplished this, I sealed the flaws in my system and re-engaged.
Everything was working fine until the giant Snail Titan showed up and smashed one of my critical floodgates for my tower-cap farm.
I love this game.