First of all, this game is plain addictive. I do not mean that in a good way. People will simply play this game for days on end. In fact, some people have died playing this game.
Addictions come in all shapes and flavors. And to date, I am aware of no Wow-related deaths from overplaying. I know of one from Starcraft, and one from Lineage.
One more obvious thing: The game isn't even any fun. Its like any other MMO.
This is obviously an opinion...plenty of people find it fun. I still find it fun after 3 70s and working on my 4th.
The effect will also take its toll on your credit card with subscription fees.
It's 14.99 a month. Do you go to the movies twice in a month? You've spent more on movies than I do on WoW. Do you have Cable TV? That costs at least twice as much, and if you have all the premium channels it costs 6 times as much as WoW. Perspective, please.
The game has caused crime. In China, one player loaned a firend a valuble item. The friend then sold it on Ebay for $1000. After that, the original guy got so mad, he stabbed his friend throught chest, killing him.
It wasn't WoW, it was Legend of Mir 3. Also within the past 6 months, Ebay has removed the ability to sell virtual items.
Also, WOW players' friends (if they have any friends) have been kidnapped by other WOW players, and demand their items. This is serious shit, guys.
As we say in WoW...Screenshots, or it didn't happen. (in other words, I'd like a link supporting this claim) As Kyro has pointed out, the vast majority of the best items in WoW are inextricably linked to their character and cannot be traded or given away, and ALL items cannot be traded once they are equipped. Well...whites and greys can, but you should be past those by level 10.
In summary, yes these games can be addictive to people with certain personality traits (OCD, Addictive personality) in varying degrees, but that's true of any activity. As a counterpoint to the Doom and Gloom in the original post, I met my wife and my best friend both while playing EQ, and the three of us still play WoW together. I've also met a good group of people who live near my mother, who I see when I go visit her..if I have the time. (mom lives near Stardock-land, and I'm in North Carolina.)
If you like WoW, play it..if you don't....don't. The world won't end either way. Do everything in moderation, being obssessed with anything is bad.