I did that trip in Oct of 2003 and loved it. First the downsides, the trip getting there was long, hot and boring, with a 20+ hr layover in Fiji. There are three cabins on the main deck (though the spirit and bilikiki differ slightly) and the rest below. Be sure to bring earplugs for nighttime as it can be a bit noisy for light sleepers. This is not for first time divers. You really should have advanced level certs, and logged a few dives to really enjoy all that this has to offer.
Now for the good stuff, awesome crews, diving, food, etc. For me a true vacation, due to the daily schedule. Get up, have breakfast, brief the dive, crew loads your heavy gear into the tinny (small boat) for a 1-2 min ride to the dive site, back roll in and go. You can stay with the DM/Guide or do your own thing. When you are done diving do your stop and surface and one of the tinny's will pick you up. The crew carries your gear back on board. Take a hot shower, be handed a warm towel, and throw on a t-shirt, grab your book and head upstairs for fresh cookies or snack of hour, read or whatever for 60-90 mins. Repeat this process all day. Usually 5 dives in a day. The night dives are done after dinner, if you want dessert they'll save it for you.
The abundance of life is mind blowing. This trip has spoiled me for other sites my dive trips since have all seemed dull. Some of the must see sights are White's landing, (stay shallow near the landing barges, forget the deep wrecks), Mary's Island - bring a reef hook, and awesome wall dives.
I do hope you have a good camera and know how to use it. I took over 2000 photos and wish I had done more. Youll need macro (nudis and pigmy seahorses) and macro for all the big stuff.
Things I liked most: can dive my own profile or stay with the DM. I would drop my buddy off and see her to the surface and picked up then continue to dive with the group until I was done.
The crew moved my gear to and from the small boats. I never had to carry more than my fins and mask.
Not having to swim back to the boat. I surfaced where ever I was and they picked me up. They have two boats in the water at all times, and try to bracket you. One will not leave for a return trip unless the other is on site. Carry a signal tube though just in case.
Food was really good and they appeared to do special meals for those who needed it.
We had the best cabin so it was perfect for my large size.
Suggestions:
Bring extra cash to by carvings, there are several stops, and they are amazing. If you don't know how to bargain, find some to do it for you. Bring odd t-shirts, cool looking watches and other "Americana" stuff to trade along with local currency.
If you have specific questions, please let me know.