Apparently, these sites and others are hosted with Amazon Web Services, who lost power at a Virginia facility last night, taking down the sites. It appears Netflix and Pinterest are back, as is part of Instagram, but some Instagram features like explore, activity and profiles still appear to be disabled for at least some users.
I am surprised that no disaster recovery system kicked in for these monster sites. It is amazing that a power outage at one facility is enough to take them down for a significant chunk of time.
Anyways, here is a bit more information about the Amazon power outage from the New York Times’ blog.