Ambrosine of I Like Bubbles mentioned being identified by the characters you play. After playing MMOs for so long I tend to echo the sentiments she makes about being known for the character you play the longest.
Never had I had so many alts as I do in WoW. Well, the other game I've played longer is EQ and to be honest, leveling a new character kinda sucked, even with items not being bound to a certain character (read: my Monk got a Fungi tunic and my Ranger had a full set of some uber something I don't remember anymore-- all before level 10).
Wow makes it so easy to just roll up a new character and get going, even with crappy newbie gear. My allotted character list is full, both with horde and alli characters.
Regardless of my characters, I'm still called Kir with the occasional naming of the character I happen to be on. Same goes for my guildmates. I still call Jerke, Sumnor, even though he hasn't played his mage since last summer.
This extends to Real Life aswell. I use game names and real life names interchangeably, and sometimes it's just more comfortable for me to use the game name instead. For others, they are more used to real life names, and often times you will hear a name or two on vent.
All of this makes this a blurring of realities in a way. Sure, EQ was highly immersive for me, but Warcraft has moved beyond and made the game uniquely special on its own.
I wrote a paper for Sociology that explains why being a gamer is part of being in a subculture. Parts of this is not exclusive to WoW however. Phrases like training, camping, agro, mobs, and the like have been part of gaming for more than a decade, and are ingrained into our language. I argue that this is not merely slang, but a separate language for us. One thing that truly makes me feel like we are part of a subculture is that our language is being adopted by the main stream. How often have you heard the word Epic to mean something truly awesome? I'm sure it can be argued differently, but as a gamer, I feel it has something to do with the millions and millions of players of MMOs of all generas influencing our pop culture.
I think I digressed a little.
For some, WoW is just a game and a social life killer. For the rest of us, it's a place to hang with friends both close and far. We get to know personalities (sometimes so well, we can spot imposters), quirks, failings and strengths. Sometimes, its like being with co-workers who you love or hate, and other times its like being in one big family (who you also love or hate)