I won't call it a social networking site. I'd call it a business-card-exchange site, plus a corporate-flyers-handout site, and of course a self-promotion site.

Selling emails is of course bad, but expecting your email that you give to any big corporation to stay private for a long time is, alas, naïve. I've read the fine print; in most EULAs it includes a ton of clauses about sharing your contacts with a bunch of third parties, etc. LinkedIn, in particular, explicitly says that it may share your contacts with advertising partners.

In other words, if you need to enter this space, wear a hazmat suit, expect no niceties.