Rhythmbox MicroBlogger is a new Rhythmbox plugin which sends the music you're listening to on Twitter, Identi.ca or any StatusNet account.
The song format is completely edibable and it also lets you edit the message to be posted so you can add context or other miscellaneous details before posting.
I found out about Rhythmbox MicroBlogger the day Twitter introduced OAuth only for all clients and Rhythmbox MicroBlogger didn't have OAuth so this post has been pending since then. But today, Rhyhmbox Microblogger finally got OAuth for Twitter so it works again!
Install Rhythmbox MicroBlogger
cd ~/.gnome2
mkdir -p rhythmbox
cd rhythmbox/
mkdir -p plugins
cd plugins/
wget http://github.com/downloads/aliva/rhythmbox-microblogger/rhythmbox-microblogger-0.4.tar.gz
tar -xvf rhythmbox-microblogger-0.4.tar.gz
Then simply open Rhythmbox, go to Edit > Plugins and enable the Microblogger plugin, then add your Twitter or Identi.ca account and you'll notice there's a new button (the Twitter or Identi.ca logo) in the Rhythmbox toolbar - click this button whenever you want to post the song you're currently listening to on Twitter or Identi.ca. Upon clicking this button, you'll be able to edit the text that will be posted.
If you want to manually install Rhythmbox Microblogger, download it from HERE, then go to ~/.gnome2/rhythmbox/plugins (create the folders if they don't exist) and extract rhythmbox-microblogger there.