seriously, why is that still brought up? it's been done and found totally useless as the whole fort grinds to a halt. Sure, there isn't much to do since you don't need to power the food and booze industry, but getting nothing done is a bit over the top.
It's only useless when considered as a fully vampiric fortress. Militia members, in particular, lose out from being turned into vampires. Professionals that aren't in a "need-it-now" profession do fine. When you're talking about a weaponsmith, who is probably something like speed 1000 (as compared to a militia member's speed 500), he becomes about half again as slow, which is easily made up for sleep/drink/eat. It's true, the long parties can be frustrating, but only when you need it done now, and you've only got a single dwarf that can access the lever-- otherwise, they're pretty much the same as for regular dwarves.
I know-- I've set up individual professional vampires in this manner. They didn't get it done as fast as non-vamps would have, but neither did I ever have to worry about their food, booze, going outside to get shot up by goblins, footrot, getting punched in the skull by a tantruming lye maker, etc. My forts are not so starved for manpower that a slight loss in efficiency is a problem. They are, however, very starved for my attention. (This is especially relevant for somebody like a weaponsmith-- I do NOT need axes OH GOD RIGHT NOW, and I do not need them by the bin-load. What I do need is for my weaponsmith to do just enough work to avoid skill rust, and more importantly, to stay alive.)
If you want an example of this, I currently have a vampire mayor chained up in his office (just forbid the chain, they'll never release the prisoner.) He gets zero work done.
Neither is he ever unavailable for meetings. That's just not possible with a non-vampire mayor.