Mojang's Notch is a smart man not just in game design terms but also in the management of the company's 20 million or so Minecraft players. The designer has published a poll on his personal blog to discover the opinions of his cuboid players. be comfortable with the company collecting various kinds of anonymous information from its players.
Mojang currently tracks only when a player logs into the game. minecraft servers list proposes to collect "non-private" data, such as the duration of the game session, OS type, whether you are playing in a single or multi-player mode and whether you are using the client or web applet. The community will then be able to access the data gathered "as usual."
Notch stated that the data will be transmitted "naturally" anonymously. It won't include your session information or user name, and it won't transmit any sensitive information you might not wish to share. To be perfectly honest, we're fairly surprised that this kind of data wasn't already collected. You can vote here to support anonymous data collection or against it in the case of the Minecraft nation.