I wouldn't say it "ruined me". But I suppose it may have done more damage than I'll ever admit. *shrug*
But on a Role-Play forum I used to be on, there was this group of people that I RP'd with. For the longest, all was cool. But I guess me being kind of... non-confrontational, they decided to take advantage of that to make the plots go how they wanted them to go. Naturally, I wasn't happy. But I kept quiet about it. After a while, they progressed from just annoying god-moders to cyber bullies. :| At this point, I started growing sick of them. So, when they pulled a fast one on another person on the forum behind her back, I told her to IM me and that I'd explain everything. From that point on, I started saying no when I didn't want to do a plot. I guess they didn't like that much. I've always been withdrawn, and therefore didn't talk to many people on that forum. My mistake, I guess. They did talk to the staff there - whereas I'd always been too afraid to even add them to YIM or anything. So, they changed chats around, manipulated conversations, and made me look like the bad one. I admit, I had gotten into arguments with them in the end - but it takes two to tango. The staff there banned me without ever even confronting me to ask for my side of the story. Just an all out ban. Few months later, they pulled the same exact thing on an admin and were caught in the act. Then, they were banned and I was invited back. Haha. I admit, I went back. But it didn't last long. In fact, I'm actually kind of... I don't know, pleased, that the site pretty much died after the bans. Apparently, it had slowly began to die after I was kicked. And then after they were and I was allowed back. Which led to them having to explain their mistake. Which didn't look good on them. So, I guess, in many ways, karma came around to them. Still did effect me in a few ways, though.
... darn internet
As far as social network sites go, I never saw the point in them. I have a Facebook, but only for family and my very few close friends. I don't bother with it outside of that. I don't bother with chat sites much any more, either.