My son Davide would classify a few of the above sites as "social networks". He is probably right. Anyway, they are far less "social" than other popular sites such as facebook or twitter. or linkedin, or ... I currently have no account in any of these. Despite owning a smartphone, I have no whatsapp account either.
Of course it feels perfectly all right staying out of these "social" tools, and keeping in touch with friends with telephone, e-mail, and occasionally skype. Plus, of course, going out and having fun together. But, since some friends occasionally ask me why I don't use such social tool or other, I'd like to say a word about this. The main reason is that all these "communication services" are provided by companies whose ultimate goal is making profit. When we send an e-mail, a file is transmitted from our computer to our partner's. End of the story. A facebook used is primarily speaking to Mark Zuckerberg, who first writes down and files away everything said, and then maybe relays it to the intended destination, if it suits him. Whatsapp does the same, plus collecting information about the user's position, activities, address book... When I activated whatsapp on my wife's smartphone and read the list of authorizations I had to give to that app, my hair stood on end!
Of course e-mails are not confidential, in the sense that hackers and/or government agencies could intercept the file sent from our computer to our partner's. If privacy is important, though, anybody can have their e-mail communications crypted using open-source tools. Even skype claims that all skype-to-skype voice, video, file transfers and instant messages are encrypted. No privacy can be implemented in social-network info transfer, which is probably all right, or it would defy its "social" purpose.
Eventually any kind of posting information to the www amounts to giving up a bit of one's privacy. For example from a peep at the EXIF details of this picture anybody can easily make sure that on Jul. 9, 2012 at 18:56 I happened to be in Gallipoli. Contrary to, e.g., an instagram post, that picture landed in the www some day early 2013, some 6 months after shooting, when all serious privacy issues were past relevance. Another important difference is that that picture is there for anybody caring to see it, not just for those inside the "instagram club". A third difference (perhaps less significant, but relevant to anybody taking photography seriously) is that in panoramio one could access the original image file with all its pixel detail (and one still can in the google archive), while social networks make a point of compressing/corrupting pictures.
In conclusion, even if you are a fan of this or that social network, and wish to get in touch with me, please be content to drop me an e-mail, or -even better- phone me...