we were talking about this with barkley's breeders when we took him back for a visit recently as his tail is a fair bit shorter than his mum's or the pup that the family have kept. we think he ended up losing about half of it if most of the pics of workers with 2/3 of their tail on here are anything to go by. personally i'd love him to have a full tail but the breeders had personally seen what injuries can occur to undocked working dogs in the field. as both parents work they assumed that some, if not all, of the pups would also do so and didn't want to risk the same injuries happening to them. i hate to think that the process caused my pup pain, and there are times when he's trying to get to the end of his tail and i feel sorry for him that he can't, but ultimately i think they made the right decision for this particular litter.
persumably it would be rather harder on a dog to wait and see what type of work it is likely to do before you dock it? i'd always assumed that they are more aware of things as they grow up and would find the experience more stressful, but i'm completely prepared to be proven wrong as i have no experience of new born pups...