[TallGuyShort]

The technology to do any of those is little more than a few database joins and some fuzzier matching logic like you are suggesting. What's creepy is just the extent to which they match. In the email contacts theory, for example, it's not hard to remember an email address that was in a user's contacts list and then suggest they connect when that email address is used. It's only creepy because you personally had no control over giving them the information that allows them to make that leap.