I’ve seen these words around a bit in reference to the Celestial Steed. At first, I thought that they were in reference to this (most excellent) wowhead comic by Noxychu. Naturally, the comic is a reference to something else. A quick glance through the comments and google search revealed that something to be a flashgame called Robot Unicorn Attack.
The music is actually Always by Erasure, and Noxychu did reference the song directly – most people seem to have jumped straight to Robot Unicorn Attack (for which it is the soundtrack) though, which is valid as the game features a faster-and-faster running unicorn that spends a lot of time aloft. It’s also rather fun, like Canabalt but more uplifting and with a charge attack. I recommend it!
(Yes, I have a celestial steed. I like it even more after playing Robot Unicorn Attack)