You can download a 300 mb file, now instead of having to do this when cataclysm is released which saves a small amount of time and will guaranty a faster start for leveling.

Open up your WTF folder in your WoW folder.
Open up Launcher.WTF in notepad.
Edit:
SET accountType "LK"
to
SET accountType "CT"
Open up Config.wtf in Notepad.
Edit:
SET accounttype "LK"
to
SET accounttype "CT"
Start downloading the 300mb update by starting Launcher.exe

I found this on arenajunkies and as far as I know this is not against the TOS.
It should help everyone to get a small headstart when cata hits