I definitely wouldn't hire someone who played for 40 hours a week, but if it's more reasonable, like 10-15, it essentially becomes a replacement for stuff like watching tv or movies.
The problem is that games like WOW are designed to be addictive, especially at the endgame levels. My college room mate ended up playing for more than 2000 hours before he quit, and it's not been great for him - he's been jobless for two years since graduation.
Seriously. I played a vast amount too -- I just did the math and it was probably around 4000 hours, a number I can barely believe in retrospect. Although I finally quit for good nearly two years ago, I feel as though the game _emptied my life_. I was fortunate to have a support group outside the game who kept me involved in recurring real-life activities, or perhaps it would have been worse.
Lucky for me, I quit the game because I moved to New York to work full time. But I've heard a lot of horror stories of people dropping out of college or life itself due to MMOs.
The problem is that games like WOW are designed to be addictive, especially at the endgame levels. My college room mate ended up playing for more than 2000 hours before he quit, and it's not been great for him - he's been jobless for two years since graduation.