I have, and it is a good way to travel if you can't stand the long flights. Of course flying business or first class will surely lessen the hardship on your body from long distance flight. There are a couple of things to consider.
1.The transpacific type of cruise you are looking for requires time on a couple of fronts. First, it will take approximately 30 days to get from Sydney (for example) to the West Coast, usually with a route that might make a couple stops in NZ, three in French Polynesia, four or five in Hawaii and then to the west coast of the U.S. or Canada. There are a lot of cruise days on this type of trip. The second time requirement is for plenty of time to make advanced planning and reservations. Those cruises tend to fill up pretty quickly, and if you don't book early enough, what is left are the more expensive cabin categories. Check 2017 and 2018 Celebrity Solstice (transpacific) from Sydney to Honolulu, connecting to the (Hawaii) Honolulu to west coast leg, and you will see what I mean. But sometimes people cancel their plans when booked this far in the future, so don't give up this far out.
2. Someone mentioned port fees and tips. The taxes and port fees show up when you reserve the cruise, so it is not a surprise, and you can figure about $12-13 a day/per person on the tips. If you closely watch the various cruise line websites and sign up for their email notifications of sales/specials you can sometimes pick up free pre-payment of tips, drink packages, on-board credits, and other perks. But, be sure to read the fine print because sometimes those "specials" do not apply to transpacific or repositioning sailings. Be sure to fully understand all of the gotchas on the perks.
3. If you do one of these transpacific cruises, you likely know that the one way airfare is usually a lot more than half of the round trip cost, and a multi-leg flight will be close to doing one way fares between you destinations. Also, if you wait too late to book, all of the early purchase seats are gone and you wind up paying a lot more money for the same type of seat.
4. If diving is your primary trip objective, you will not have too many really good dive opportunities during the 30 day trip over or back. Get your diving done before or after the cruise, and then realize you are only going to have a handful of dive opportunities during the cruise. Personally I found the diving in Fr. Polynesia to be so-so, and you are only in Maui and Kona for a day each as a rule, and sometimes the arrival times are not very compatible with the early departures of the dive ops. Shore diving is a pretty good option at both locations.
5. Cruising is a fairly inexpensive way to travel if you consider the cost of lodging, comfort of the room, the huge quantity of food available, and on-board entertainment that is included.
6. You are going to gain weight unless you are a dedicated, avid gym enthusiast.
If you have any specific questions, feel free to PM me.