Here is the Wikipedia entry on them - Last.fm - Wikipedia, the free encyclopedia
And here is the actual website - Last.fm - Listen to free music with internet radio and the largest music catalogue online

Its a pretty good site and once integrated into the dashboard and as long as its available in game then it should be an excellent feature, imagine creating a custom playlist and then all listening to it while playing in game... Should be a pretty cool feature and could expose some peoples dodgy taste in music!

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