Hurrah! Spotify have released a native Linux player which works with free accounts!
These notes show (which are mostly for my benefit) show you how to install it and configure your multimedia keyboard so the play/pause key controls the music on Spotify.
Download Spotify for Linux. It's available in 32bit or 64bit.
Double click on the .deb that has been downloaded and it should install. Nice and easy!
sudo apt-get install xbindkeys
Create the default configuration file for xbindkeys.
xbindkeys --defaults > ~/.xbindkeysrc
Edit the configuration file for xbindkeys.
Add these lines:
"dbus-send --print-reply --dest=org.mpris.MediaPlayer2.spotify /org/mpris/MediaPlayer2 org.mpris.MediaPlayer2.Player.PlayPause" XF86AudioPlay "dbus-send --print-reply --dest=org.mpris.MediaPlayer2.spotify /org/mpris/MediaPlayer2 org.mpris.MediaPlayer2.Player.Stop" XF86AudioStop
Run xbindkeys to see if it all works
Now, when Spotify is running, pressing th eplay/pause key will make your music start or stop.
You will need to set xbindkeys to run automagically on startup.
On Ubuntu, System -> Preferences -> Startup Applications.