My brother-in-law just had an aft balcony on the Conquest this summer. The pros, he says are you do not have other people smoke, you have a great view of the wake, and a little more privacy. The cons? Well, you do not have as much air flow which is bad in the heat of the summer. Some say that there is more movement in the aft and forward cabins, but I have never had too many problems with it. The other upside is that you are below the Lido and can sneak up on a quich bite with ease.
I personally would love to have an aft balcony.