The most oft-quoted conversion figure is from the Industry Retailer, which pegs the average e-commerce conversion rate at about 2-3%. However, this study by Smart Insights digs much deeper into that number. For example, look at their chart on Conversion Rate by Referrer:
What you’re seeing here, is the power of intent. On AOL, Bing, Yahoo, Ask Search or Google, people are actively looking for a product or solution. This makes them more likely to buy the product when they find it. On Facebook, Pinterest, Twitter, LinkedIn, and StumbleUpon, people are passively browsing. They don’t have the same intent to buy, and therefore convert at a lower rate. Product Hunt fits in this category. People browsing Product Hunt aren’t going to the site looking for a specific solution; more often, they’re checking the site out of boredom.