I don't see an Audioscrobbler plugin in the Rhythmbox 0.9.1 I an using now, but
if I remember correctly there was one added in more recent versions.

Audioscrobbler/Last.fm constructs a user profile based on what the listener
listens and by comparing the music listened by other users that have similar
music "taste".  A wonderfull application of this is Last.fm radio: after having
built the user's music profile, he can listen to radios corresponding to his
music tastes.

The "problem" is, those radios can only be listened from the official Last.fm
player.  I personally don't like to have lot of apps loaded at the same time.  I
think it would be great if Last.fm radios could be listened directly from inside
Rhythmbox.

I read that this tool might be useful to achieve such a feature:
http://vidar.gimp.org/lastfmproxy/