Update: 4/21/2014 05:22 PMUTC
All sites are now up, the root cause appears to have been a required index was not replicated out to the FE SQL machines. We have manually applied the index and all sites are responding as expected.
Initial Update: 4/21/2014 04:28 PMUTC
The primary MSDN, Technet and VisualStudio.com sites are currently offline. DevOps teams are fully engaged and working to restore the service. We apologize for the inconvenience and will update you in the next 60 minutes.