WoW will not "ruin" you. I have freinds who play it and they are perfectly normal. Well i admit that some people play it way too much, but that can happen with ANY video game.
I don't actually think World of Warcraft will ruin your life, however it can if you don't know where the line between reality and video game is. I can devote over 5 hours to a single sitting of FFXI, City of Heroes or Ultima Online but I still go to work, eat, shower, watch anime/TV shows and read comics. But people who devote their life to it, those are the ones who will be ruined by it.
I do, however, think WoW ruins the MMO community as a whole. Now it's all about high rate, high levels and devoting all your time to raids or instances or whatever they've added. I played the game, and people tell me that "the game really begins when you hit the level cap" well you know what, screw that. I want the game to begin when I hit character creation, that's why I play FFXI, City of Heroes. And I absorb myself in Ultima Online because I think it has one of the best communities in MMO's, even if it is over a decade old.
I am not nor will I ever be interested in WOW. Where I live, pretty much everybody who plays it is stereotyped as a nerd with no life. And seeing as it would be very difficult to persuade people otherwise, I think I'd rather keep my life rather than sell it to WOW.
I tried to play wow but i didn't like it but my friend does and he has no life but that"s only cause he has a addictive personality. People who play Wow can be normal