I just looked back in my blog archives. I published my “level 80″ post on December 22nd, 2008. That is 39 days after the Wrath of the Lich King was released.
I finally reached level 85 last night, December 23rd, 2010. That is 16 days after the release of the Cataclysm expansion. Keeping in mind that this time around I had significant real life distractions, leveling in Cataclysm was really, really short. And I am one of the last people I know to hit 85.