Stumbled across this the other day (well, GF did actually), apologies in advance if its known or a repost.
When she created a new Pandaran (Shaman, if the class happens to matter, I dont know), got it to 10, picked a faction and then used a Scroll of Resurrection to get it bumped to 80, she was able to use both the purple Griffon and Wind Rider (as Alliance). This seems to be some sort of bug with the instant-80 bump and Pandaran factions, and there were no restrictions at all as far as we could tell.
She then transferred this character to another server, and the Wind Rider was gone. Apparently there's some bit of logic there that checks for things like this.
Nothing earth shattering, but I figured someone might enjoy playing around with it. I only had one account to try this on too, so if anyone tries it and can confirm it, that would be cool.