I began using Last.fm almost two years ago. Although it hasn’t changed my listening experience it’s been interesting to observe my listening habits, plus I’ve met several people that I’ve found are my musical soul-mates through the site.
Foremost it’s a music networking site. If used regularly it may open you up to the discovery new music. Your homepage will recommend new artists to you based on what you already have in your library. You don’t need to visit the site often. Last.fm will “scrobble” everything you’re listening to without you ever having to log into the site. Also, if you happen to own an MP3 player your plays with add your plays to your library on Last.fm after it’s finished syncing.
I would recommend Last.fm to people who really love music.