It looks like Bing is trying not to clutter the UI with its social features by default:
"Sidebar is the most novel component of the new Bing. It's a mellow, gray sidebar that is closed by default. It shows a thumbnail of your picture and two control icons, and that's it. There's a hint arrow to expand it. When you open Sidebar, it shows you stuff from social networks that's relevant to your search."
It looks like Bing is trying not to clutter the UI with its social features by default:
"Sidebar is the most novel component of the new Bing. It's a mellow, gray sidebar that is closed by default. It shows a thumbnail of your picture and two control icons, and that's it. There's a hint arrow to expand it. When you open Sidebar, it shows you stuff from social networks that's relevant to your search."