I know this has been suggested before, but I really must reiterate.
After a recent encounter with the Eerie Glowing Pits, I was a bit underwhelmed with the result. I had intended to write up a story based on the fate of the fortress after its encounter with demons and adamantine, but the situation broke my sense of immersion horribly.
I could carry on with the long story, but there were basically two things that seemed ridiculous. Knowing there were demons, there was no way to actually get all of the military on call. I stationed 5 squads, and only one was reliably on station at a time. I actually was fortunate that, by the time the demons arrived at the entrance to the exploratory shafts, two other squads had started to arrive on site -- though one was probably going to hare off soon after. However, in the meantime haulers were racing into the mines to pick up random stuff -- which lead to the loss of four or five dwarves who were doing nothing better than hauling loots, as I hadn't forbid the entire, long stretch of the mines.
What would be great would be fortress-wide alarms, as elements of the standard orders. One, 'Alert Status', would compel military dwarves to stay on station, even if they grow hungry or tired. Further, it would be handy to designate whether a squad 'rallies on commander,' or 'rallies on station,' so that you can decide whether you prefer whole teams on site, or whether part of a team is better than none. This way, when it gets to be critical, the dwarves don't just hare off to have a beauty nap when there's a swarm of demons snacking on your peasants -- and even if they do hare off, you can decide whether the entire squad hares off with them.
The other would be an 'Alarm' or the like -- which would compel civilian dwarves to flee to meeting halls or similar places of the player's designation, and drop all non-essential tasks. This way, we don't need to worry about those silly situations where civilians try to march into the path of an invasion to pick up a goblin's recently dropped +cave spider silk banana hammock+ or the like. I mean, seriously. Most of the time, dwarves behave in a pretty reasonable manner, so far as simulation's concerned. But once you introduce enemies, it just starts seeming weird. :/