I just posted this on avc.com, but might as well add to the discussion here:
Songkick (http://songkick.com) nails this for first time users.
You can go to the site and start tracking favorite bands without providing any sign up info. Only after you have tracked a reasonably large number of bands and you're invested in your list does it ask you to sign up.
(I'm not affiliated with them, I was just impressed by the workflow)