After my post describing how to get all Google+ profile URLs I got some comments claim there is no an issue here. Ok, I’m gonna to explain now what’s the issue.
Some profiles contain mails e.g. check for (“my mail” site:plus.google.com) in a search engine. Even if 0.5% of all profiles stating email, it’s more than 2M quality mail adresses(with Name and Family, interests, website etc).
Some profiles contain website URL so it’s possible to gather site owners database too(to promote domain- or hosting stuff etc).
The same is true for other marketing databases possible to be gathered at Google+.
In case of other social networks, it’s not so easy to gather data even if profiles are open to spiders, because it’s almost impossible to gather millions of URLs through search engines even with advanced querying techniques. So profile sitemaps is the real privacy issue.