LinkedIn creeps me the hell out with their connection suggestions, that are way too accurate for for anyone to make through honest means, especially given that I've intentionally been very restrictive with what I've added to my profile. I've even been very uneasy about accepting connection requests, since this isn't something I really want to contribute to.
Of course, that means the cost of deleting my account is very low given that I hardly use it in the first place. Something to think about.
Yes I'm always surprised by who shows up as suggested contacts. Often it's people who I've interacted with online maybe once. My best guess is that those people are providing LinkedIn their contact lists.
If you supplied your email, you have given LinkedIn everything needed for honest, accurate suggestions. They used the suggested contacts' address books.
I have a problem where I lived in a building with a bunch of people who turned out to be fairly dishonest. We all have each others email addresses because we had to communicate about the home-owners' association. I moved out, and now LinkedIn regularly suggests that I connect with these douchebags because I'm still in their address books.
LinkedIn once suggested I connect with a neighbor in my apartment building. All we ever did was say hi to each other, we didn't know each other's names. The only reason I knew the connection suggestion was about this person was because of the photo. That was a WTF moment.
I'm guessing if they don't get enough hits by matching email addresses and address books they go one level deeper in the graph. That would explain some of mine.
Of course, that means the cost of deleting my account is very low given that I hardly use it in the first place. Something to think about.