I agree with James that this lens is hard to justify for a cropped sensor body, where the excellent 17-55mm is more versatile. Also in the places I usually dive this lens ona DX body doesn't cover a particularly useful range (although I expect it to be my main lens on my forthcoming Bahamas trip).
I got mine in 1999, I think, and it is a lens that I plan to never sell. It is that sort of purchase.
Many quote this a Nikon's finest lens, but be careful when buying second hand as this lens was/is popular with photojournalists and there some heavily beaten up examples out there. If you get a second hand one it may well be worth paying for a Nikon service?
The lens is very sharp, but it is the rich colours it captures that always marks it out for me. I can instantly see the difference in my pictures when I use this lens. It is a class apart from the 12-24mm and the 18-35mm nikkors and you see it in the photos. It is why I have never bought a 12-24mm.
But I don't think that this is a lens that finds too many subjects underwater. And I use is sparingly. Of the 200 pictures in The Art of Diving I took 12 with this lens. I took over 100 with the 10.5 or 16mm.
Alex
p.s. congrats Sarah on your victory.