While Linkedin and Ryze get all the business social networking glory, they don't facilitate referrals the way that they should be facilitated (IMHO):

Tell-A-Pal is a trusted referral system based on a simple premise: If you are a service oriented business or professional, your greatest source of new customers are your existing customers. So why not reward your existing customers for referring new customers? It makes sense. Tell-A-Pal makes it easy.

Here's an example. That's the way TellAPal do.

Found via Business Pundit.

If anyone tries this out, let me know.