I went with my lower 80 team (pal-4xshammy) with about a 3500 gearscore average to Hyjal and just quested for four hours with tons of waiting, and I mean tons.

With no BOA gear on I got about 70% into 80 before giving it a rest and starting my all Worgen mixed team which I got to level ten in about an hour of questing.

In beta it was much faster leveling a single toon but I'd rather my toons stay the same level.

Lots of green quest rewards were huge upgrades for my lowbie level 80 team. I have yet to take my 5500 average gearscore mixed team to the expansion.