The mount definitely drops off the Valentines boss, according to Wowhead's data-mined feat of strength "Big Love Rocket."
For those of you who, like me, don't have people to run you through this year (or if your character isn't 80 yet), try to hold your dancing guts down so you don't have a heart-attack. I know every sensible person will want (nay, NEED) the rocket, and that includes you, but do yourself a favor and try to not wake up in the middle of the night stressing that you'll have to grind forever to get one. There are other years to get this puppy, even if it means waiting for everyone else in the world (of Warcraft) to get one so that you can roll uncontested.
Personally, I'm waking up in the night thinking "I want a pink mount nao!" But I have to remind myself: "Self, you has a phoenix. Chill. The Valentines boss is not going anywhere, family group is leveling to 80 on casual alliance alts, and you'll get your pretty pink mount on Birdy and Windwhistler if you're just patient and don't freak out."
Then I pat myself condescendingly on the head and go back to sleep.
Boss: Apothecary Hummel
Where: Shadowfang Keep (Silverpine Forest)
I don't have specific details on the fight or where he is in Shadowfang Keep, but you can be sure there will be some info available the very first day, usually on Wowwiki.
In the meantime, please feel free to look over last year's Valentines notes if there is anything you may have forgotten, and as usual I'll have changes and notes up for this year once the holiday starts.
Also, good luck with Peddlefeet this time around, everyone!