My stated goal is to have 9 level 70's by the time Wrath hits. As you can see from the sidebar, I'm 7/9. The last two I have sworn to only level with their appropriate Boon-alt-companions.
In this case, Karika the resto shaman with Diathim the enhancement shaman, and Karitei the fire mage with Kenshiro the feral druid.
An added aside, we only really level Karika and Diathim with a real life friend of ours, who is playing a retribution paladin named Vialora.
Just three days ago, Karitei was in her mid-50's. And then boom, suddenly Boon decided, "I want to rawr." and so we dusted them off, stuck them in quest-rich areas and BOOM, before we knew it, we were running the familiar paths of Hellfire.
Maybe I'll get my goal completed.
Boon asks me, "What are you going to do when all your characters are 70, and you have no one to level with me?" ... that's what power leveling is for, my friend! And PvPing. And quest-reward-hunting. And instancing.
Too bad they don't let you start DK's at level 1. Because I'd so do that.