I currently use Foobar to play my music library; the last.fm client to play custome radio streams from my friends, or based on my past listening habits, etc - and Songbird for mp3 blogs (I love the way it lists all mp3's on a page on the standard music library format, with easy download links), and to check the Songkick plugin. If songbird was lighter and snappier, it could take on all of the above functions for me. Hopefully as it nears 1.0, a lot of work'll go into optimisation and streamlining