Bill St. Arnaud finds: The Flattening Internet Topology: Natural Evolution, Unsightly Barnacles or Contrived Collapse? by Phillipa Gill, Martin Arlitt, Zongpeng Li, and Anirban Mahanti. The full article can be found here (pdf).

In this paper we collect and analyze traceroute measure- ments1 to show that large content providers (e.g., Google, Microsoft, Yahoo!) are deploying their own wide-area networks, bringing their networks closer to users, and bypassing Tier-1 ISPs on many paths. This trend, should it continue and be adopted by more content providers, could flatten the Internet topology, and may result in numerous other consequences to users, Internet Service Providers (ISPs), content providers, and network researchers.