My Take
Minecraft is a virtual world where users can decide what type of world they want to create. Participants use various tools to create buildings, signs, landscapes, etc. Minecraft even has an educational version now that has a library of worlds, levels and activities that support a variety of subjects and allow teachers a bit more ease of use to deliver content in this virtual environment.
How I Use It
So far, I have just let individual students play and develop worlds. They end up using a lot of creativity and problem solving when playing. The 2 modes I have seen students use are Creative Mode and Survival Mode. In survival mode, students have to gather all their materials to build, craft ,and gain experience points. You could assign students to re-create a particular time period, or create a scavenger hunt or game where inside the world there are challenges to answer. You can actually link to websites from inside the world so there are endless possibilities. In addition, when building, students learn architectural and civil engineering concepts. Because there are animals and plants, and geometric figures to be built, you can incorporate almost any subject. I know a language arts teacher who used it with low readers at high school level and saw more engagement than seen in the past just because of Minecraft. See the minecraft edu wiki for more ideas. http://minecraftedu.com/wiki/index.php?title=Main_Page They have a lessons Activities section to help.