As a persuasion tool, social proof is fantastic.  Customers can really resonate with other customers feedback.

Try using testimonials directly from customers, Twitter or Facebook feedback or even full blown case studies.

They need to be believable, relatable and timely.  One of the biggest mistakes in our opinion is that sites use social proof from months or years ago.  Keep it updated and relevant.

"See what our customers say about us..."
rather than
"Choose us because we're great and..."