Cruise bumping is not like flight bumping in that when a cruise ship cancels your reservation, unless it is for mechanical problems with the ship (covered by most policies), there is ample time to reschedule another cruise.
The problem with the Rosie O'Donnell situation was that this ship was leaving out of NYC if I am not mistaken. NYC has far fewer ships to chose from then say, Miami or Port Carneveral. Again, this cruise was cancelled a few months prior to sail date so besides the initial disappointment, there was plenty of time to find another cruise during that same week.
I think the vast majority of reservations that are bumped are those that have been booked far in advance before the various organizations have made their request to block out entire ship/decks.
You can't prepare for the unforseeable. You have to just roll with the punches.
Also, I would rather be bumped than to be put on a ship that of booked 75% or more of the ship to any special interest group (don't care which interest).
(cruzin' solo by design)
Freedom ('09), Imagination ('08), Victory ('08), Destiny ('08), RCCL Navigator ('08), RCCL Majesty ('08), Glory ('07), Liberty ('07), Fantasy ('07), Destiny ('06), NCL PofAm ('05), Fascination ('04), Victory ('04), Fascination ('04), RCCL Voyager ('03), Fantasy ('99)