Fomo (formerly Notify) is an app that rotates a banner with the details of recent orders. They have pretty substantial claims on how this type of social proof increases conversion rates. I tried it for a few days and it didn't do jack as far as I could tell. I'm not going to write them a bad review because that was hardly a scientific test.
My customer demographic is 45-65+ years old - perhaps that's why my customers didn't "jump on the bandwagon?"