I'm off on a 9 night South Pacific cruise in 6 weeks with our then 10 month old. Ill pop back and let you know how we go but from a travel agent point of view they are very popular.

I've booked hundreds of families on them and they are a huge hit! You unpack once and get to visit lots of places. Be aware though that they are really strict on kids swimming, no swim nappies and kids must be 100% toilet trained to go in the pool.
Amy, which cruise line are you going with? All the cruises we looked into wouldn't allow children under 12 months. I'd love to know the ones that take littlies!