I leveled 5x hunters, to level 60, during my RAF time.
They were quite fun, but have been on the back burner since then.
I'm planning on getting them to 68th level shortly, for 5x more alchemists.

Chances are you'll need seventy-something, for maximum trade-skill levels in Cataclysm...
So getting them to 80th isn't a bad idea.

Overall a hunter team is quite fun for leveling.
I was running 5x Beast Mastery team.
Very simple to macro and the pets are powerful.
Did not do instances with them, aside from a short stint boosting to have the other four catch up to the existing hunter.

Concussive Shot on round-robin.
Frost Trap on round-robin.
Pet Intimidate on round-robin.
But most of the stuff is just, everyone shoots and pets go wild.
I was using Keyclone at the time, I'd imagine Volley with the IS Boxer mouse broadcasting will make for some very fun AoE too.

I wouldn't think they would be good in instances.
But with flying mounts across the board, probably Slow + Cold... since this is a team I'm not gearing or playing long-term...
And two pieces of heirloom 10% experience gear.
I'd think this will be as fun in the new leveling grind, as they were during RAF.