As awkward as it sounds, I think MMOs provided opportunities to gain the confidence and the verbal skills necessary to be successful socially. I was never really a normal kid--if you looked at how I spent my time as a kid, you would have thought I had an Asperger's like obsession with history and geography. Hey, I'm not complaining, since it made for some great moments!
Throughout my time in WoW, I went through several phases:
Oblivious, innocent kid.
And I guess I turned into a pretty normal young adult after that. Still weird, but in good ways. I could always improve though. =)
While there's a lot of social interactiosn that MMORPGs cut out, like physical health, body cues, etc., and MMOs can never replace interacting with people in real life, you're still interacting with other people in a meaningful way. Cultivating relationships, building an image, lending your skills to other people, having fun, etc. As a reclusive, introverted teenager, MMORPGs kind of gave me an opportunity to bloom, first in the virtual world, and then in real life. I wasn't really afraid of socializing, but I just never saw the point until I made the connections that I did in WoW.
At the very least, it gave me opportunities to make an ass out of myself in a context that didn't matter, so when the real life comes along, I wouldn't fuck myself over when it counts.
EDIT: now that I look back, I was really easy trolling material when I was 12. I remember engaging with some dude in trade chat, that I later learned was an infamous server troll, and saying "yeah, uh, I don't know if I can really say what my sexuality is until I've had sex". hahahahahaha goddamn little me
I'm glad I didn't take things seriously back then. It helped me make more friends than enemies.