We just might have seen the first public hack that will cause people to die or be physically hurt. Homosexuality is illegal in certain countries (like Saudi Arabia) and this hack might expose people to harm in these countries. Some reactions of spouses might also be violent.
It looks like the reaction of most commenters is very different compared to when Gawker exposed the Conde Naste executive. This hack might have done this very same thing to many people.
On one chat website (I'm not sure if it's a good idea to post links) people are already requesting emails/domain and others are providing them. This can be used for blackmail, revenge, or to contact spouses. There will certainly be divorces resulting from this. August 19 will be the day when many people's lives were overturned. I don't know of any other hack that had such an impact in the past.
Apparently, the emails listed in the leak did not require user's confirmation, so people are posting a mix of fake and real emails. I don't know if the email confirmation flag was included in the hack or not. This could easily result in people who were not involved in any way with the website to become falsely implicated.
I don't see how Ashley Madison can survive this. They will surely be sued by multiple parties. This hack also supposedly shows that fake female profiles were used. Hacker's message calls it a scam with 90%-95% of users being male. This is a company that just a few months ago was thinking of an IPO and of raising $200 million (http://www.bloomberg.com/news/articles/2015-04-15/adultery-w...).