I have, more than one time. You have to be able to stand up to the high pressure sales pitch and believe me it will be high pressure. Depending on the terms of the "free" you may have an unbelieveable bad cabin with bunk beds in a noisy location and there may be blackout dates. Also, many times there are major restrictions as to whom you can make your reservations through and they will have limited access to cabins. You could find it very hard to book a cruise on a date anywhere near where you want to go and when. I have found it usually not worth the aggravation.