I've done a few of these and they are lots of fun. One thing to remember if it's your first time cruising - is that the service on a turnaround is not likely to be as good as if you were on a week long cruise. The cruises tend to be full (because of the cheap prices) and the crew don't work as hard - because the tips just aren't there on a turnaround.
And yes - I know for sure, as I was crew on two RCCL ships and service lacked on these voyages.