Metaphysic, a dwarf priest in the guild Afterlife on Cenarius, posts screenshots of himself at level 70, along with his /played. A long thread consisting of doubtful screenshot analysts and people who don't understand the irony in calling someone else a nerd on a video game forum ensues.
Asked how he did it, Metaphysic said he solo quested all the way to 70 in 44 hours. He's gotten 11 hours of sleep since the expansion's release. He'd already been to 70 in beta, so he mostly knew where the good quests were -- although he did say there were some "brutal" periods of griding when he couldn't find a good quest.
I created a character on Cenarius to see if I could confirm this, but Metaphysic wasn't online (unsurprisingly.) The screenshots look pretty darn convincing, though, and since a ton of other people in his guild were 67, I wouldn't be surprised if he really was 70.
So congratulations Metaphysic, and as your guildies said, get some sleep!