Level 3* has partitioned its part of the Internet from Cogent's part of the Internet by denying Level 3's  
customers access to Cogent's customers and denying Cogent's customers access to Level 3 customers. Level 3  
terminated its peering with Cogent without cause (as permitted under its peering agreement with Cogent)  
even though both Cogent and Level 3 remained in full compliance with the previously existing interconnection  
This means a whole host of issues for a lot of people.  
more here:  
foobable: Hasn't Cogent had this problem before (AOL T/W)?