Tried  last.fm for the first time. shell-fm[1] feels like a reasonable
 client.

 I'd love to keep using MPD[2], though. I don't quite know yet how  one
 is  supposed  to  use last.fm with MPD. All I can do is add a bunch of
 songs to my playlist but that's it. How do I do continuous playback?

 Well, last.fm-support in MPD is in a pretty early  stage  anyway.  One
 has to use mpdscribble[3] or another client to "scribble" songs...

 ____________________

 1. http://nex.scrapping.cc/shell-fm/

 2. http://mpd.wikia.com/wiki/Music_Player_Daemon_Wiki

 3. http://mpd.wikia.com/wiki/Client:Mpdscribble