Apple has just introduced iTunes 8 -- and with it, a Pandora-like feature called "Genius." Here's how it works: You pick a song in your library and hit the "genius" button, and it creates a playlist based on the one song. You can then copy that playlist to your iPod.
I randomly tried two songs two songs this morning as a quick test, starting with "Neighborhood #1 (Tunnels)" by Arcade Fire. Pleasantly and predictably, I heard Wolf Parade, Bright Eyes, David Bowie and Jeff Buckley. When I tried another random song in my library -- "It's Over" by Roy Orbison -- it seemed to just pull any '60s tune it could find, so I wound up with The Electric Prunes and The Seeds; good songs, but not in the spirit of a song like "It's Over." But then again, it played Roxy Music's "Virginia Plain," which was a brilliant choice in some odd way. Orbison had a unique crooning style, and so does Roxy Music's Bryan Ferry.
Genius works by looking at the songs you play and the songs you skip. It analyzes the data, along with all the data from everyone else in the world who uses iTunes and Genius, and picks artists it thinks you'll like. The more people use Genius, the better it should work.
If you use Genius or Pandora or any other playlist generator, I'm curious to hear what you've discovered -- the strengths and weaknesses of each -- and I'm always intrigued by the quirks.