Dustin Curtis:

After an investigation into the problem by Facebook’s data team, they discovered that the new News Feed was performing too well. It was performing so well from a design standpoint that users no longer felt the need to browse areas outside of the News Feed as often, so they were spending less time on the site. Unfortunately, this change in user behavior led to fewer advertisement impressions, which led, ultimately, to less revenue.

Boy, it must be great to work as a designer at Facebook.