My wife and I, along with some friends, took a cruise from San Diego to Cabo, Mazatlan, and Puerto Vallarta, from December 13 to December 20, 2008, on Holland America's Oosterdam. This a chronicle of the trip.
We left from Tucson, AZ, on December 12, and drove to San Diego, staying with some friends. I think from now on that that is how we will do it, going in the day before. It is less stressful in that if something happens, you have a day to deal with it and you won't miss the boat.
On December 13, embarkation day, we arrived at the terminal right at the busy time. The line was long. It took us about 45 minutes to an hour to get through. Funny thing, though, someone recognized us from my wife's Cruise Critic avatar, and came up to us in line.