From time to time, Carnival notifies travel agents (and sometimes past guests) of their "One Day Sales". If you book a cruise on that day, you are usually eligible for free upgrades and additional savings.
Text:
Just because summer is coming to an end, that doesn't mean your plans for an unforgettable vacation have to end too. This Thursday, August 28th, is Carnival's One Day Sale and we're giving our guests FREE upgrades and BIG savings on virtually every cruise sailing between now and August 31, 2009!^*
It's 24 hours of savings, and the perfect day for you to book your next cruise. Just remember, these amazing offers are around for one day only. Be sure to book your cruise Thursday.
More information here.
Feel free to let me (or another travel agent) know if you need more information. When you get pricing, make sure to include all fees, port charges and the newly increased fuel surcharges ($9 per guest per day based on double occupancy; additional $4 per guest, per day for third, fourth and fifth guests)

