Here are the instructions and results:
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 76 related artists for my profile are Alanis Morissette Ali Farka Touré and Ry Cooder Amadou & Mariam Aretha Franklin B.B. King & Eric Clapton Beck Björk (2) Blind Faith Blondie Bob Dylan (3) Boubacar Traoré Brian Eno Brian Eno & David Byrne Bruce Springsteen Buddy Guy Can Coldplay (2) Cream Crosby, Stills, Nash & Young David Bowie (2) Elvis Presley Emerson, Lake & Palmer (2) Eric Clapton Explosions in the Sky Fela Kuti Fiona Apple Frank Sinatra Frank Zappa (2) Franz Liszt Frédéric Chopin Garbage Genesis (2) Gentle Giant Grateful Dead James Brown Jethro Tull Jimi Hendrix Johann Sebastian Bach Johannes Brahms John Lee Hooker Kate Bush King Crimson Led Zeppelin (2) Marvin Gaye Mogwai Muddy Waters Nick Drake Oasis Pere Ubu Pink Floyd (3) R.E.M. (2) Radiohead (3) Rush Sarah McLachlan Sergei Rachmaninoff Simon & Garfunkel Stevie Wonder Sting Sufjan Stevens The Allman Brothers Band The Arcade Fire (2) The Beatles (5) The Doors The Police The Residents The Rolling Stones (3) The Smashing Pumpkins The Smiths The Velvet Underground The Who Tinariwen Tom Waits (2) Tori Amos U2 (2) Van Morrison (2) Yes
Some observations:
It seems like the Beatles, the 'Stones and Pink Floyd are "similar" to just about anyone from the '60s--including each other. That, of course, is a rather weird thing to say; Last.fm's saying it, though, keeps me from achieving eclectic Nirvana (80). 76 isn't too bad, though.
Ah, well. I suspect that my good friends Fearful Syzygy and Mozo have me beat in the eclecticism department anyway.