You may not have investigated the site enough to have found it but we have an easy to use Meet On Board feature. Check it out, fill in your cruise info, and besides hopefully finding other cruisemates on your trip, you'll be included in the Bon Voyage wishes when your ships sails http://www.cruisemates.com/CF/MOB/index.cfm
BTW... this is NOT posted to discourage anyone from posting on the boards to find fellow cruisemates. In fact I encourage you to discuss your cruises on the boards when you find fellow shipmates.
Just another tool!