Yesterday we talked about social networks that harvest the address books of registered  users and send mail to all those addresses on behalf of their registered user. In the specific case, the registered user did not know that the network was going to send that mail and subsequently apologized to everyone.
That is not the only way social networks collect addresses. After I posted that, Steve mentioned to me that he had been receiving invitations from a different social network. In that case, the sender was unknown to Steve. It was random mail from a random person claiming that they knew each other and should network on this new website site.  After some investigation, Steve discovered that the person making the invitation was the founder of the website in question and there was no previous connection between them.
The founder of the social networking site was harvesting email addresses and sending out spam inviting people he did not know to join his site.
Social networking is making huge use of email. Many of my new clients are social networking sites having problems delivering mail. Like with most things, there are some good guys who really do respect their users and their privacy and personal information. There are also bad guys who will do anything they can to grow a site, including appropriating their users information and the information of all their users correspondents.
It is relatively early in the social networking product cycle. It remains to be seen how much of an impact the spammers and sloppier end will have. If too much spam gets through, the spam filters and ISPs will adapt and social networks will have to focus more on respecting users and potential users in order for their mail to get delivered.

Deliverability • Permission • Spam