http://www.southernxreptiles.com/Article PDFs/q&a_species_together_lr.pdf
I think the article by Doc Rock (simon stone) is excellent and sums up the risks and dangers well..
i hear so many people say "I have my two together and they are ok" etc and I also keep a few together myself without any problems.. But all snakes are individuals and you cant base assumptions on a small number of success stories that all snakes will be ok together.. theres definite risks and you should know your snakes well before attempting this.. personally I'd never house sub adults together of any species.
the only animals I ever keep together are adults that are breeders or fully mature and then only in certain instances as I know the snakes. theres still a risk but Im pretty sure they will be ok otherwise Id never do it.. the rule of thumb usually is... If in doubt - then dont..