The title said it all.
You can’t fly in Northrend before level 80 on release - you need level 77 and the skill (buyable in Dalaran at level 77).
On release, we took the zepplin in group for Borean Toundra. After that, we ported 3 others players and 1 player that was on flying mount.
When summoned, the player didn’t lost his mount. He was mounted and in air, and could fly in Northrend at level 70.
To prevent a ban, we asked the player to remove his flying mount instantly. But you can be sure that lot of players exploited that 
. Easy mining, easy herbs, easy time lost protodrake, accessing zone earlier.