Blizzard has changed the server downtime to encompass all of today and most of Friday.

Nebu's Post (http://www.worldofwarcraft.com/thread.aspx?fn=wow-general&t=423793&p=1#post423793)

Its also on the Community Main Page over at the WoW Beta site.

I think some of the other gaming companies threatened to do horrible things to Blizzard if they didn't give us Beta Testers a couple days to go and play other games.