[ajj]

This was exactly the thought I had while reading Patrick's post. What if the sign-up page on the website has a link saying "Ask my friends (on FB, twitter, whatever) if they can refer me."

When people look for jobs, this happens often. Someone you know well works somewhere and you ask him/her to refer you. This makes it much more palatable, I believe even more than the double-sided incentive.

Of course, the downside being only people who end up on the webpage will do this. The double-sided incentive actively seeks to find more customers.