From time to time I get a connection invitation at LinkedIn.
Sometimes I have no idea who the inviter is, and have to ask "Sorry, where do I know you from?" Some other times, it is from a well known name in the industry, and I certainly know of or heard of the person, but I do not recall ever communicating with that person.
I feel honored to be invited, but I do not know how I deserve that honor.
Social is hard for me. That is probably because, as Linus said in his Google TechTalk on git, "we are geeks and we have only two [friends]" ;-). I end up keeping links only with people who I have first-hand experience communicating with, either in person (old colleagues) or in ether (git community members).
Perhaps other people are more casual to connect promiscuously. I dunno.