I was on the Pirate's Lady June 2005, and I LOVED IT, going back again this June.
As for what to expect, it is definitely not a luxury cruise, but is an experience that can't be compared. The berths are tiny, but you don't spend much time in them anyways. The food is great, the cook has like a 3x3 area to cook in, and turns out great food. Most everyone we cruised with gained like 5 pounds that week, no kidding.
The water temp is like bath water, unless you are cold blooded you could easily dive without a suit, but I would recommend at least a skin. I took my 3mm, mostly for protection from fire coral and such, but I dove bare a couple of times anyways (and got bit by the fire coral...which was an itchy experience for about 3 weeks...)
The showers are pretty much a no go once you are cruising. They have one, but the freshwater is really limited. They have a hose up on deck that feeds from the air conditioning condensation tank which we used to rinse off after every dive, and to "bathe" with. It's not treated water so you can't drink it but it's serves it's purpose as a makeshift shower. If you have long hair, I would definitely invest in some quality hair conditioner. I have really long curly hair, and I would put conditioner in my hair after every dive, and rinse with the hose. Since they do about 4 dives a day, trust me, you will have dread locks by the middle of the week if you don't do this. I took a razor that has the shaving cream and the razor all in one, and just sat on the ladder at the back of the boat and shaved my legs. Did I mention that modesty is not a quality needed on these boats?
I would bring at least one extra pair of sunglasses too, one guy had his break on the second day of the cruise....
Pack lightly, you pretty much have a shelf and the floor to store your stuff. You really live in your bathing suit the whole time, so a couple of pairs of dry shorts and tees and one cute outfit for port night is really all you need. They do have outlets and mirrors in the rooms for hairdryers and such, which you might want to use on port night. They do have bathrooms and showers at the docks in Bimini, which you are more than welcome to use for free, but there are only 2 in the womens and 2 in the mens, and there is probably going to be at least one other boat docking at the same time you do, so you do the math, the good thing is that there are not a lot of women on these boats, so it's usually the men waiting for a hot shower. I skipped the last dive on port night and took that time to use the boat's shower and to get all prettied up, so while everyone else was waiting in line for showers, I was buying souvenirs and making phone calls. Speaking of phone calls, if you will be calling home while in port, you should bring calling cards with you. There is like two pay phones on the whole island, and the little market area closes after dark.
You can also bring your own CDs, otherwise you are at the mercy of everyone else's musical taste....trust me on this one.
The only money you will need is for port night, tips at the end of the cruise for the crew, and souvenirs. At the end of the cruise, you can purchase a map that one of the crew has plotted out every where your boat traveled. It's pretty neat because it's all yellow looking like a treasure map.
I can't say enough good things about the crew, they were really great, down to earth guys. You will love it!!! Let me know if you have any questions, and good luck!
Oh, one more thing, you definitely need extra batteries for your camera and flashlight. I would invest in some rechargeables.