Social Music etc - Last.FM , Rhapsody , Digg , Del.icio.us

Is anyone using Last.fm or any other social music service? Do you use Rhapsody or Yottamusic? For that matter is anyone using Digg or Del.icio.us?

I just started using last.fm... it's currently keeping track of everything I listen to on windows media player or iTunes, and building out a music profile for me that it can make recommendations against. Unfortunately it doesn't always work in catching the music, including if I replay an album that I've already seen it catch. Is this a fluke?

Are there other social oriented sites that I'm not using that I should give a shot?