We recently put out a very major new release of Goombah, which incorporates a number of "social networking" features that were absent before. We've added a built-in messaging system, the ability to see other people's most played artists, and much more.
Also, I'd like to mention again that you can hear most recommended tracks in Napster by clicking on the little speaker icon to the left of each track. Not just a 30-second sample -- the whole thing, completely free.
Check it out. Let me know your thoughts.