Most obscure artists...
Last.fm calls me "Underground" for Martin Best Medieval Ensemble... LOL
So, here I am ripping CD's this week that we bought from groups we've seen and I hit all the top scores. I am a bit surprised that my friend in Brazil is ahead of me in the most obscure since many of the groups I've been adding to my library are only "Portland, Oregon USA" groups. But then I also see that many of my plays are not scrobbled to Last.fm and I'm not sure why. Mainstream albums are, but the local productions are not always, even when they have a barcode uniquely identifying them. Last.fm probably has a database that screens scrobbles to only those they know about. Also, some of the music store promo discs are not scrobbled.
So, Last.fm is not really a true measure of the music you've been playing, but better than no measurements.