Zappos make approx $3.50 for every $1 they spend on Facebook advertising

"Facebook ads work for us. We’ve spent about $10 million over the past two years at about a 3.5:1 ROI. About 99 percent of that spend has gone toward direct-response ads driving traffic to Zappos.com. If we were to look at Facebook ads on their own, a 3.5 ROI is not sustainable and is well below our overall direct-marketing program’s ROI expectations. But when we consider where Facebook ads fall in the sales funnel and compare them to similar marketing efforts (mainly category-head search terms), they deliver similar performance, fuel other channels (drive long-tail search and comparison-shopping queries), and are one of our best marketing channels for driving new customers."

Source:  Nate Lurman of Zappos, interviewed on Digiday, 28th June 2012