Just to be clear... as far as I know most of the people who started this thread did not sit through a sales presentation. They were just responsing to mailers that said "you are eligible for a free cruise, call now."
In some cases I have "won a contest" for a free cruise. One contest I won twice! (what are the chances?) and a friend of mine also won (incredible good fortune!!).
Most "free cruises" (if there is such a thing) are turn-around cruises to Nassau were you sail and arrive the same day. Then they stick for hotel fees, etc.
If you are already into this for $175 apiece you may have already paid for 1/2 the cruise (assuming they plan to give you the lowest category cabin). I have no doubt at some point they will tell you about the government Taxes & fees that you are responsible for.
Then there will be special fees for "preferred sailing dates." Then there is the upgrade fee if you decide the hotel/stateroom you are awarded are not to your liking.
In the end, it will cost you as much as if you just booked the cruise straight up. They make their money through all the people who just walk away and from what they sell. It's sad really, but nothing in life is free.
What people need to know is that cruise lines like Carnival have no need to give away free cruises (their ships already sell out). Therefore, no one who is offering a free cruise got that cruise for free, and that means there is no way they are going to give it to you for free.