The idea isn't necessarily new, but a recent article on O'Reilly Radar by Marie Bjerede is one of the better ones that seeks to first understand how games like Warcraft and Minecraft are engaging and attractive, and second how to bring those elements into the classroom.
As it pertains to Warcraft, Ms. Bjerede leaves almost no area uncovered. Goals = grades, the game = school, and leveling up is the vehicle to success. Early on in her critique she mentions using a type of "unlocking" of new content, similar to how Warcraft functions, and something that has some merit. Students right now are guided through content at a set pace and a set order, but in a effort to provide ownership and autonomy, she suggests that students be able to proceed at their own pace, unlocking whatever they think the next content is they're ready for. Of course, this doesn't mean jumping from basic math to calculus; each subject would be split into smaller, but related, modules.
She goes on to examine the role of group dynamics within the game world and how those can fit nicely with such an approach to education. Be it guilds or your basic dungeon run, players not only need to know the basics (say, what we learn in school), but also how to apply those basics using higher thinking and collaboration (like the real world).
All in all, it's an intriguing article, and one of the better analyses presented recently. Minecraft is thrown in there to address another side of education, that of promoting exploration and curiosity, while not knowing just how things will turn out. This is a nice marriage with what she shows Warcraft can provide, as the real world requires knowing the basics, how to use them efficiently and collaboratively, while also having to stretch beyond what you know sometimes into the unknown.
This little blurb only scratches the surface. Check out the article at their site.