Heh, sorry to be here with problems again, but it seems it doesn't recognize all songs. More often than not, it returns a "TRACK does not exist".
A few examples of songs that does NOT work:
spotify:track:1CrdVjtoizXBQhTYQa8Fr5
spotify:album:6MDeMi4c1Zo1KRKtCgZpsb
http://open.spotify.com/track/4GA1uSb2gqYk2JBURBNQf8
spotify:track:2vttkA1GXyIsLwv0BLEXvS
spotify:track:23Wqpr9sQ43vOMuYOnf3vq
http://open.spotify.com/track/4kPjHePWXQyzD5pLpZJlHx
A few examples that DO work:
spotify:track:39B9GhCjnwcpBl2nbbGULk
spotify:track:480dDrqG7LO6qDaphHeXlM
http://open.spotify.com/track/6cuuWMASwMSSLDPoK8NrIY
http://open.spotify.com/track/4liUIZvPF9E1I2CTAuNcr5