I used Sky Auction to purchase a December, 2003, 7-day cruise on the Carnival Paradise (smoke-free ship) out of Miami. Since I was traveling solo, I had to pay twice my winning bid ($201), plus one set of port taxes and handling fees. I got a cabin to myself for a week for $603, all inclusive. I saved about $200 off of what I could have otherwise purchased the cruise for through a travel agent. And although the bid only guaranteed an inside cabin, Carnival upgraded me to an outside cabin. I was very satisfied with my Sky Auction experience, and with the cruise. But like any other auction, it is essential that you determine the value of what you are bidding on first, so that you don't overbid.

By the way, you will probably get more responses if this thread were moved to either the Travel Buzz or Travel Bidding forums.