Here's a simple script to show the currently playing song in Spotify. All you have to do is put it on your $PATH and run:

> nowplaying
The Unsinkable Fats Domino by Guided By Voices

While this is handy in and of itself (to some people), if you are running GNU Screen, you can have it output the currently playing song in your statusline. Just add the following to your .screenrc:

backtick 101 5 5 /home/YOURNAME/bin/nowplaying
hardstatus string  '%101`'

If you already have a hardstatus (or caption) line, you'll just need to add %101 in there somewhere. Then, you'll have the currently playing song easily available.

For info about what the above does, see the GNU Screen manual about backtick.

Here's the entire script:

#!/usr/bin/env python
"""Spit out the currently playing song."""
import dbus
import sys

try:
    bus = dbus.Bus(dbus.Bus.TYPE_SESSION)
    spotify = bus.get_object('com.spotify.qt','/')
    info = spotify.GetMetadata()
except dbus.exceptions.DBusException:
    print('Spotify is not running')
    sys.exit(1)

track = {}
trackMap = { 'artist'    : 'xesam:artist',
             'album'     : 'xesam:album',
             'title'     : 'xesam:title'
             }

for key, value in trackMap.items():
    if not value in info:
        continue
    piece = info[value]
    if isinstance(piece, list):
        piece = ', '.join(piece)

    track[key] = piece.encode('utf-8')

if track.has_key('title') and track.has_key('artist'):
    print('%s by %s' % (track['title'], track['artist']))
else:
    print('No song playing')

If you want Spotify to use the built-in notifier in Ubuntu, then by all means check out Spotify-notify. It also adds support for media keys.