I've had issues with elevators that stop working for no apparent reason, but last night I was able to duplicate a break. If a mob is standing on the elevator when it is triggered, the elevator will break. And in some cases I've been unable to get the elevator to work again. I like the elevator effect and the resource requirement, but I would support a move to something different for three reasons. First, elevators seem to break unexpectedly (I don't think mobs are the only cause). Second, they are useless in high lag situations, and can even get players stuck, forcing a log out. And third, they can be used to generate infinite sand (a weak argument I know ). Craftbook's lift sign is less useful (does not support multiple floors), but the way it "teleports" players does seem to avoid a lot of the problems that the elevator mod exhibits.
Actually, it [CraftBook] does support multiple floors, albeit with 2 signs per floor and going down one floor at a time.