Well, this is interesting. Bing ran a test, placing links to Facebook, Craigslist and eBay underneath its result for google.com when the user searched "google".
Matt McGee at Search Engine Land noticed what he thought was a bug, until he received confirmation from Bing that it was actually a test (which has since ended, apparently).
Regularly, if you search "google" on Bing, the top result will look something like this:
You'll get Deep Links (Bing's version of what Google calls Sitelinks) for Gmail, Images, Maps, News, Videos, Translate, Documents, and Finance. In other words, you get links to various Google services, which makes sense. You also get an actual Google search box.
In the experiment, however, users would see half of the Google deep links, and the other half would be for things like "Go to Facebook, Go to YouTube, Go to Craigslist, and Go to eBay. Well, YouTube is still a Google service, but why in the world would someone searching for "google" want any of these?
McGee has a screen cap:
Essentially, Bing was sending users to Google competitors. You may not always consider sites like Facebook Craigslist or eBay competitors to Google, but Google has a social media service, and it has a shopping service. At some level, Google competes with all of these sites.
I'm surprised they didn't just put a "Go to Bing.com" link there, or even a "Go to Yahoo.com" link. At least you can still access Bing results from Facebook.
McGee posted a Q&A with Bing about the test. He asked how Bing would respond if a search for "bing" on Google included Sitelinks to Twitter, Amazon or Kayak. Bing's response was, "We appreciate all customer-focused innovation."