Nothing that has gone to date will come close to the strain placed on the infrastructure of video delivery like the inauguration of Barack Obama as the 44th president of the United States.
Almost all of the news outlets, from Fox and CNN to the NY Times are planning to carry it live.
It has to be remembered that CDNs are next to useless for live event delivery (unless reconfigured) - their servers exist to replicate content closer to the viewer, which isn't optimal for live delivery.
The Internet is a great way to deliver video, but, pending the wholesale upgrading of its infrastructure to IPv6, it's not the best way to deliver live video to huge audiences.
Bandwidth Day will be the ultimate test of how far the Internet's infrastructure has come.