Last.fm is powered by the Audioscrobbler system, which is essentially a database that tracks user listening habits and does a multitude of things with statistics. The great thing is that every single song you play from your computer can be potentially "scrobbled" into your Last.fm profile.
What this means is that any music (or even dynamic music e.g. streams) will be tracked in your profile, and you can go back and see every song you've ever listened to on your computer, or even your iPod. Last.fm sorts all of these tracks into a nice readable format, where you can see what your most listened to tracks were for the week, the month, any given day, and so on. See pic for my recently played songs;
Based on your listening habits, last.fm will recommend similar artists and tracks you should check out. This alone has allowed me to discover a ton of new bands with no research at all.
Head on over to LAST.FM and make yourself an account, it is totally free and completely worth it if you want to discover some new music. Also, feel free to leave me a comment as I am slowly approaching my 100,000 play milestone.
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