I just came back from this and if you are into live music of the amplified blues variety, I highly recommend it. www.bluescruise.com
is their website. There are two cruises a year. Basicallly it's nonstop music and jams almost 24/7 for a week. I went to the Caribbean - I'm going on the next one in October leaving from San Diego.
The musicians are fabulous and are name brands (so to speak). The whole week is casual - shorts in the dining room - and fun. I haven't gotten so little sleep in years - but I had a fabulous time.
I'm not trying to plug it for the company - the cruises tend to sell out completely (without my help). And people become LRBC uh... groupies? They go to them over and over so there's a group of people that you get to be friends with and see once or twice a year.
This is, alas, not cheap because of the cost of having so many bands on board. But it is an intimate concert experience and loads of fun.