Write any freakin' journals.
Take your top 20 artists. For each of these artists, collect the top 5 similar artists. The resulting number of unique artists is your eclectic score. If the score is small (extreme = 5) your musical preferences are very limited, and if it is large (larger than 80, extreme = 100), then you have an eclectic musical preference. You can compute your own score at http://anthony.liekens.net/pub/scripts/last.fm/eclectic.php
My eclectic score is currently
The 90 related artists for my profile are Alexisonfire, Amon Amarth, Antioch Arrow, Arch Enemy, At the Drive-In (2), Atreyu, Bane, Black Flag (2), Cannibal Corpse, Casey Jones, Children of Bodom, Circle Takes the Square, City of Caterpillar, Clikatat Ikatowi (2), Cursive, Dark Tranquillity, Death Cab for Cutie, Destroyer, DragonForce, Dream Evil, Explosions in the Sky, Finch, Foxhole, Frog Eyes, Funeral for a Friend, God Is an Astronaut, Godspeed You! Black Emperor, Heroin (2), Hot Cross, Hüsker Dü…