Here is the current state of the Minecraft Server:
(1) Single player and Server are combining into the same distribution. Soon the Single Player game will be sending data periodically to snoop.minecraft.net over HTTP (not SSL) during single player gaming.
(2) The following information is collected by the server process in v1.2.5
os_name <- reported from Java process
os_version <- reported from Java process
os_architecture <- reported from Java process
memory_total <- reported from Java process
memory_max <- reported from Java process
memory_free <- reported from Java process
java_version <- reported from Java process
cpu_cores <- reported from Java process
players_current <- reported from Minecraft server
players_max <- reported from Minecraft server
players_seen <- reported from Minecraft server. Dunno the math behind it yet.
uses_auth <- reported from Minecraft server: online / offline configured
server_brand <- from the Minecraft server code: "Vanilla", etc.
(3) The IP address and network details are available to Mojang through the data posting process.
Here are some things to consider:
A) Location information is available based on the IP information. Take a look at what Google Analytics can work out based only on your IP address. Network details, geographic area, ISP, etc. What demographic do you fall in? The cost-conscious member of "ISP A" or the prepared-to-pay-a-premium for "ISP B"?
The iPad/iPod/Android editions are apps which have GPS capability. What could this mean? Take a look at this (admittedly alarmist) video:
C) Your gaming habits are being tracked.
D) Lots of kids play Minecraft and the community is up to 26 million strong at the moment.
Where Mojang could take this:
i) Improvements to release and build management based on physical system information. New platforms like the excellent "0x10c" can target the biggest platform opportunities.
ii) Advertisement delivery. We have demo mode now. The conversation goes like this "We have 26 million users, and can tell you what city they live in, how often they stare at our screen, and when they are home. Would you like to advertise your pizza delivery service with us? How about gym membership?" ;]
iii) Changes to the licensing model for the server. Mojang has made commitments about your client ID being a one-off-payment. What could be possible with the information above? I could license the Minecraft server by concurrent clients, named user, number of CPU Cores, monthly activity, etc.
There are more opportunities than this and if you are a company in growth mode, you are considering them all (Mojang - call me if you need a hand will you? ;] ).