Started OW training late '05, certified early '06, so my observations are based on the past 16 years. Some of these points were noted by others.
1.) Solo diving has been clawing its way up to public awareness and respectability.
2.) Dive tables have gone from 'on the way out' (albeit with a lot of fussing by some die hards) to a rarely mentioned relic.
3.) I agree nitrox has become more common.
4.) Some dive destinations I used to rarely hear of have become better known, at least on ScubaBoard, judging from posts. Mainly Curacao, but St. Croix and the Cabo region of Mexico.
5.) I agree 80-cf tanks still dominate, but a number of providers at some varied destinations offer at least a limited number of 100-cf tanks (albeit some filled to around 3,000 PSI, not their rated fill pressure of 3,300 PSI, so for practical purposes more like 90-cf tanks), and a few destinations have really big tanks (e.g.: Jupiter Dive Center in Florida and Olympus Dive Center in North Carolina had 120-cf steel tanks).
6.) Dive computer interfaces have improved in terms of being more intuitive. Some now support Bluetooth and I've heard of some connecting wirelessly with smartphones.
7.) It seems physical log books used to be mentioned more often and presumed to be kept (though I think many people didn't). These days, not so much. Many people who want a log use a computerized log.
8.) Shark feeding/baited diving seems to've grown in public awareness on ScubaBoard, awhile many people still wouldn't choose to participate and many are still opposed, the degree of acceptance and tolerance has grown. It can now be brought up sometimes with automatically triggering a multi-page headed debate.
9.) In the wake of the Conception disaster, I am more conscious about liveaboard safety issues, particularly a backup exit in case a fire blocks the usual exit, and I think many other divers are, too.
10.) At least on ScubaBoard, I think awareness about the BP/W option has grown even for recreational divers not aiming for tech.; on the other hand, at many dive destinations, the jacket style BCD seems to rule.
11.) The recent closing of Guadalupe, Mexico as a great white shark cage diving destination is big, as it was pretty much the only game in town in the larger region. I never made it there.