This hack compromised a bunch of people. It’s a little different from previous compromises/breaches. The impact to people for most of those previous efforts was largely in the PITA category; sometimes people needed to lock their credit, or work with banks to recover stolen money.
This is a bit different in that the results of the breach could affect marriages and relationships in a very direct manner that undermines what trust those relationships have.
Supposedly the reason for the breach was disapproval of the site by the breachers. That would be, I think, the first large-scale breach done in the name of morality, as opposed to ideology or financial gain.
It has not taken long for sites to be set up to search the purloined data. The media, ever a sucker for a quick sex-related story, has breathlessly reported a surge in calls to attorneys. Who knows if that is true, but I suspect the potential is there.
I heard a panelist on a program state that if people wanted to visit sites like Ashley Madison, they should buy a throwaway phone, get a throwaway email, and the like. I don’t know how many types of site like A-M are out there, but there are thousands of porn sites at least. I would suspect they are targets of attacks like this as well.