Stumpy is right. They will come back up when Blizz feels they are ready to be online again.
Seriously people...it's a stress beta. Blizzard said specifically that they were testing to see how much stress the servers and infrastructure can take. So YES there will be lag, YES there will be servers going down. It's not like you are paying for it, and they extended until Sunday for the Stress Test. You KNEW what you were signing up for...or maybe you didn't. There seem to be an inordinate amount of people on this stress test that seem like they didn't pass remedial reading comprehension.
Please let this thread die and no more threads about the servers and when they're gonna be up or complaining that they are down...I come to these forums instead of the stress forums to get AWAY from all that.