But please, do not put this on your resume as one of your skills, or as leadership experience. Some people do this, and it generally just gets them laughed at.
Perhaps the people laughing are just doing so because they are brought up thinking gaming is a waste of time, or just a fun activity that has no other meaning in life besides entertainment. There is probably not much to learn about real world activities in a corporate environment by spending 16 hours a day playing Super Mario Bros. 3, but MMORPGs like World of Warcraft or Guild Wars are entirely different. You're not just playing a game where you have complete control over the situation (if you jump on the Goomba, the Goomba gets squished). You're interacting with perhaps hundreds of people, with different levels of skills and abilities, who all may or may not be working toward the same goal - a goal that one single individual may not be able to complete on his own.
In a game like WoW, you can track the stats and abilities of your guild members, decide who is good at what and where they should position themselves or what each person should be doing in a raid to get the best possible outcome. In a software development company, you can track the skills and abilities of your team members, decide who is good at what and which types of tasks (hardware interface code, design documentation, GUI design, networking code) each member should be assigned so you can produce the best possible piece of software. It's not about just running out there and swinging a sword at the bad guys for hours on end.
The same skills in WoW could be brought to sports. Lead a football team to victory by positioning each player where they best fit and tracking metrics from this. Should leadership in sports not be used in a resume?