We bought a cruise on the MSC Opera Jan/05. I found that skyauction worked on their timetable and not yours. While the cruise documents 2 weeks or so before the cruise, I would have like to have had them earlier.
We paid for an inside cabin on a specific date and that is what we got, essentially a Guaranteed inside, it was forward, one cabin from the bow of the ship.
I would use skyauction again, and always beware of the additional fees compared to the cost of purchasing a cruise through the normal channels. For us everything went fine from the skyauction perspective. Having looked at winning bids and not necessarily cruises, there are bargains to be had.