Anyway, here's some kind of meme, I think.
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 91 related artists for my profile are Al Green, Alanis Morissette, Amos Lee w/Norah Jones, Aphex Twin, Aretha Franklin, Armand van Helden, BeatFreakz, Beyoncé, Bob Dylan (3), Britney Spears, Bryan Adams, Camille, Cat Power, Chris Rea, Damien Rice, Daniel Moynahan, David Bowie (3), Destiny's Child, Dido, Duke Ellington, Ella Fitzgerald, Elton John, Elvis Costello & The Attractions, Eric Clapton, Faith Hill…