He doesn't go into specifics about what will be updated, but we have some good guesses at what we could see included:
- Achievement listings
- Wrath of the Lich King items
- New reputations
- Faster character data updates
means that you have to log into your character to repopulate the Armory information on it. This is important if you have seldom played alts yet still refer to the armory data, or if you are currently applying to a guild that requires armory information.
We'll have more concrete information on what this update brings after it's complete, sometime around 2 p.m. PST.