The implications go deep...

My son gets big mad when my daughter accidentally plays pop music on his account and suddenly his suggest songs are all "girly music".

Now you can play your guilty pleasure song without your crush or gym buddies finding out because your suggested songs are now additionally weighted by what your friends share.

WoT doesnt always have to be based on a friend graph either... other metrics can be applied. Especially if you cam "rate" other users in terms of how close they are to you in music taste. These ratings can then propagate and create a music wot matrix parallel to the social wot.