Group Cruise Experiences

Hey all, was wondering if anyone has had any experience planning a group cruise? I'm looking to set one up for a bachelor party sometime next May. One of NCL's 3-day weekend Bahamas cruises sounds perfect, and I'm seeing rates around $250 for an inside stateroom. Does anyone know what kind of discount(s) we might be able to swing if booking anywhere from 8-15 staterooms?

I've read stories of free rooms for the group planner, free cocktail parties, and/or extra on-board credit... but I'd like to hear some slickdealer comments on the subject. Thanks!