We haven't actually shown up on the pier expecting to get a ticket, but we rarely book beyond 90 days because we've found the prices to start dropping as it gets closer to departure day. We usually book about 60 or less days in advance. But then we are very flexible about days and itineraries we sail.
I've often wondered why cruiselines don't have "standby" categories just to sell those last remaining cabins at a bargain price. Those of us close enough to drive to the ports would love to get those last cabins at rock bottom prices.