I've been back in the hobby for a little over two years now. Last kept saltwater in 1998-2002 high school/early college. I was w/o tanks for about 10years due to moving for jobs. When I got back in the hobby, everything was different -far more advanced & fish that were once thought to be "hard to keep" weren't much of a problem anymore.
Saltwater in particular changed. Live Rock & RO/DI are now mandatory. I had never heard of a sump or drilled tanks 10 years ago.
LEDs, pythons, canister filter advancements, Prime/safe - fishkeeping is a breeze. Much more enjoyment, less work & way fewer lost fish.
But the internet is definitely the reason for the advancement in fishkeeping IMO. Out of the fish I currently keep (all freshwater) I had never heard of them in 2002. All info about a species can be found on forums(this forum & Simply Discus I read daily), importers or breeders can get you any fish you want(delivered to your door) & you can find tanks on the cheap on Craig's List.
In the coming years, I expect sump technology & new ways of doing quick water changes to see this biggest advancements.