And by relationships I mean friendships / acquaintances etc... not the romantic kind.
It's really quite strange when you think about it. With the launch of Mists of Pandaria I have just spent most of the last 36 hours (while I was awake - I'm not that dedicated) with a group of people who I most certainly consider friends, but at the same time could knock on my door and I would not know them from Adam.
Some I might recognise from photos but even the more extroverted have only posted a few (a handful at most) and so I would need to go back and check to be sure.
Some I might recognize if I heard them speaking. But even then I have never heard any of their voices that haven't been digitally encoded, sent hundreds of miles, decoded and reproduced by my speakers or headphones, and people never really sound the same in person as they do on the phone. Plus if they have something distinctive about their voice (like a strong accent) anyone with the same characteristics will sound the same at first. Case in point I raid with a Dutch guy, and I used to work with a Dutch guy with a similar strength accent. In my head they sounded the same, although objectively I know if I ever talked to them together they would sound completely different. Not all x group sound / look / act the same, but it's a natural memory short hand to only store the most distinctive information. - no scientific basis whatsoever for that statement.
And then their are those that are more security conscious people who I only know through an Avatar and a nickname. Over my time online I have spent many hours communicating, playing and raiding with people who could live next door for all I know. There is absolutely nothing wrong with this - in fact I respect the discipline of those who manage to maintain the integrity of their online privacy. But it does lead to some odd results I my crazy brain.
In the absence of certain information my brain just makes s#1t up. Completely unconsciously I find myself picturing and (what's the auditory equivalent of picturing?) dubbing these people over as real life analogues. So online friends with similar names to real life acquaintances suddenly look and sound like them in my mind's eye. If someone is unique and distinctive enough personality / name wise but the play a tall blonde human male warrior, take on the build and facial structure in my mind's eye. Young ladies who have a similar sense of humour to a real life relative become a cousin in one's mind.
And now that I really think about, I think I'm OK with my illusions. It would be great to know many of these people more / better even IRL, but I suspect in many case the mental image would be over written. In a sense my friends would cease to exist, and even though a real life interaction could well be more meaningful, I think I would mourn the loss of the person I got to know in the first place regardless.