We've done a lot of posts about the popularity of gaming over the last decade. The video game industry has been bigger (from a revenue standpoint) than Hollywood for a few years now. Teen boys are most likely to be addicted gamers and have been known to play for hours on end.
This video came out a few weeks ago about a kid who played World of Warcraft for almost 5 years straight. The video is him deleting his profile, and every charter, virtual good and item that he gained during that period. It's well done and quickly went viral.
The game mentality is something that is extremely interesting - specifically around levels. Getting to the 'next level' breaks down your task into smaller chunks. You focus on one task, accomplish it and then move onto the next one (almost like episodes of a TV series). Where games get addictive is the quest for the next task, the next accomplishment and the next character. It's a form of storytelling that is extremely interesting, and addictive.
I remember as a kid playing Final Fantasy 6. At that time, the game kept track of the amount of time that a user spent. When, one day, I read that I'd spent 220 hours playing, I figured that it was about time I went outside. Not many games (as far as I can tell) actually put trackers in like this one - like Casino's with window's, if you know how long you've been playing, you might not care about getting to the next level.
Link here to the story.