I'm wondering to what extent Social Proof helps the Conversion Rate of websites and marketing.
Specifically I'm wondering what effect Social Proof would have on Conversion Rate for a sample task in an online context. Lots of marketing material espouses it's effectiveness but I would like academic research on the matter.
There's some basic research I've found that shows yes, people do things their friends do (such as some of the studies referenced in the Wikipedia article) but this is not specific to new methods of Social PRoof.
What quantitative research has been done in regards to social proof effects website conversion with modern Social Proof techniques like Facebook likes and Amazon customer reviews?