Vampires can be fun, they let your dorfs to hunt the most dangerous game. Especially so in a traditionally mined fort where everyone has their own bedroom and there are no communal sleeping areas, even the hospital rooms have their own sleeping/treatment units. Had 2 vampires at the same time in one of those kind of forts, around 10 people were drained in total by the two of them. First one was caught after 6 kills or so and had all the deaths in the fort blamed on them. It resulted in several hundred days in jail and 500 hammerstrikes. The vampire survived about 300 hammerstrikes before I switched to a stronger hammerer. They didn't last through all 500 after that.
The second vampire just went insane, getting a loooong jail sentence instead of a lot of hammerstrikes. Cloth rot ruins the FABULOUS fashion sense of vampires. Oh wait, there was a third vamp, that never seemed to get anyone. Mainly because they were in the military, and without a danger room, AND they were a part of the steel wearing crossbow squad. As result, they were already pretty slow. They became slower and slower as time passed. I don't know if they managed to drain anyone, with everyone waking up before the vamp had time to creep their way to the room, but it didn't really matter that much. They took a spear to the head in a siege.