My experience with MUVE games is a bit small. I've played SIMS and also Animal Crossing, both I found very fun. Animal Crossing is definitely one of my favorite games I've ever played and would recommend it to people thinking of playing. If you've never played you're basically the only human in a world of animals that act like people. You go about your day like you're living it for real, you even have a job and can interact with your neighbors.
I see the use of MUVE by libraries for long distance learning opportunities. Being able to store information in a digital library on a plain like Second Life would give the users the ability to learn in their gaming world as well as the real world. I'm not very familiar with how Second Life works but I understand that people can do things as if they are in the real world. Having the possibility to go to a library would also give users to go someplace that is beneficial for the real world as well as something to do in the game. It could also serve as a nice meeting place and could offer different events like book clubs and collection exhibits.