I have to admit that I don't see the point of so-called social networking sites, but I recognize the possibility that some people may find them useful, and I am just not one of them. Nevertheless, I still fail to see why random people I have never met want to add me as a contact. I get invitations from these people on LinkedIn almost daily, and to make it worse, LinkedIn then sends me reminders about them. Note that I am not even registered on their damn site. I don't have a profile, and I have no intention of creating one.
Which presents another problem: I couldn't find a way of opting out from these invitations without creating a profile. Clever, isn't it? They send you spam, and then they are trying to sucker people into registering to stop spam. I could just start marking these messages spam, but I think that my spam filter would take a while to learn this, and in any case, I don't want to add noise to the Bayesian model just to create false positives for relevant e-mail. The cleanest solution I found is putting the whole linkedin.com domain on my blacklist.
I want to emphasize that this is a rare distinction: with spam filters getting so clever (thank you, Gmail!), I haven't had to manually blacklist a sender in years. Congratulations are in order: dear LinkedIn, you are a really obnoxious engine for spam! I sincerely hope that you vanish to oblivion soon.