I played WoW from launch until about a year out from launch. It didn't destroy my marriage, but it wasn't great for it.
I have seen 3 different marriages go under due to WoW, even couples who played the game together eventually drifted into their own groups in the game itself and fell apart.
I'm not saying it happens to everyone, but I do see a lot of situations where it happens and the person playing WoW doesn't even see it happening until it's pretty much too late.
WoW itself isn't inherently any worse than any other game, and they have made pretty substantial strides from what I hear in lessening the amount of time it takes to grind to higher levels. I would never go back to it though. Like any MMO, it is more prone to take a part of you out of your "irl" life, and it can cause pretty substantial harm to social and family life if not kept in check.