I spent eight years with Nekton, and overall I thought it was a wonderful experience. It is not for everyone, as evidenced by the high turnover rate. That being said, the dive industry is transient by nature so people tend to leave resort based jobs almost as frequently.
PLUSES:
1. The diving. I logged over 2500 dives while working on the boat, most in my first four years (after I got my captain's license there wasn't as much time to dive).
2. An opportunity to save money. IF you enter the job with no bills (no credit card bills, car payment bills, mortgage, etc.) there is an opportunity to save a decent amount of money. We used to work nine weeks on/three weeks off, so essentially there is nowhere to spend any money for nine weeks. Some crew members would blow there entire earnings during their three weeks off, but I managed to squirrel away quite a bit.
3. Gaining sea-time to get your mate's/captain's license. The "real" money in working on a liveaboard is working as a captain. After a few years you can take your USCG exam (if you are a US citizen) and your pay will go up. It will also open up lots of other opportunities--in diving and outside of diving.
4. Travel. Aside from getting to dive and explore your boat's itineraries, your off time is an opportunity to travel (especially if you don't have a house or apartment to go home to). While working I got to travel throughout the Caribbean and Central America as well as lots of trips to North Central Florida for cave diving.
5. Picking up dive related skills. Most liveaboards are looking for volunteers to pick up photo and video pro duties. These skills will help in your later dive career. You might start out as a novice, but by the time you leave you can be an expert. There are also opportunities for picking up seamanship skills such as driving skiffs, navigation,
6. Meeting lots of wonderful people. Through the years I met lots of crew members who are still my friends today. Living, eating, and working with folks for months on end is an opportunity to form lifelong friendships. I also developed great friendships with many of our guests and still correspond/dive with some of these folks to this day. I saw thousands of guests during my eight years on the boat, but I can count on one hand the number of absolute "jerks." Most guests are out to have a good time and very few are difficult to work with.
MINUSES
1. It is hard work. Expect twelve hour days (and often longer) for weeks/months at a time.
2. Non-diving responsibilities. As an instructor, you may still be required to work as steward (cleaning guest rooms and laundering towels) one day a week, work as a galley assistant (helping the chef) one day a week, and do night watches (monitoring engineering) a few days a week. Many go into liveaboards thinking about the "glamour" of being a dive instructor only to be humbled by having to be involved in the day-to-day operations of the boat. Personally, I liked being steward and galley asst., because those were the days I got to dive on my own time, without teaching or leading dives. But many of our crew absolutely hated these days.
3. Turnaround days. I can't speak for other liveaboards, but on Nekton we did Saturday-Saturday cruises. That means that the old guests get off in the morning and the boat has to be prepared for the new guests coming on Saturday night. The boat has to be thoroughly cleaned, fueled and provisioned, which leaves you virtually no time for yourself during the only day in port. This was by far my least favorite part of the job.
4. Boat maintenance. Not everyone likes to scrape and paint, but it is necessary on a boat. Often repositioning weeks (when we move from one home port to another) are spent doing lots of HARD manual labor. Nekton tries to keep people employed during its yearly shipyard/USCG inspection, so expect a few weeks of dirty, nasty work (I don't know other liveaboard policies).
Overall, for me the pluses outweighed the minuses and I enjoyed my time spent with Nekton. There are cetainly some negatives, but the truth is that ALL jobs have there crappy attributes. Bottom line, I spent many days working on the dive deck and thinking to myself I can't believe they are really paying me to do this.
If you have any specific questions, please feel free to PM me.