Thanks to Bill P. for calling in about a major outage at Cogent.
Looks like it affects all of their major peering points:
keynote internet status

Cogent Network Status Page (currently not responding).

Brian Krebs (Washington Post) was able to confirm the dual cut with Cogent. See his blog for details.

Update (13:30 EST, 18:30 UTC): Keynote now reports some improvement. But traffic within the Cogent network appears still to be out for the most part. Note that 'cogent.com' is not associated with Cogent Communication. The official website is 'cogentco.com'.

The Cogent network got cut at two different locations. One around New Orleans and a second in  Washington DC. Appears that only the New Orleans issue is a fiber cut, while the Washington DC outage is caused by faulty networking equipment inside a data center.