Diving appears not to have damaged me at all! The tropical sun, however, has left me a bit pink and freckled. Hopefully this indulgence every once in a few years won't be the cause of my cancerous downfall.
Diving was quite interesting. The feel of my ears equalizing was satisfying in some odd way. Being able to move about three dimensionally was dreamlike. We went as deep as 18 meters in our five dives. (The first three dives were with the instructor, practicing some skills.) In truth, the most interesting reef life was visible closer to the surface, due to color and lighting. Though, deeper, we did get to see a manta, a five-foot shark, and some meter-wide giant clams.
(By the by, if you do end up in Cairns snorkeling or diving to see parts of the reef, check out "Reef Teach", which is a little edutainment show all about fishes and corals of the reef. Great slide show and informative and entertaining narration.)