Users in roles with the "view referral source statistics" permission will be able to
view the Referral Sources Statistics page in Content Management. Administration -> Content Management -> Referral Sources -> Statistics.

It gives basic stats. Totals for each referral source selected/specified for the entire site and for each area where the referral sources prompt is shown. I might expand on this further but probably not too much unless someone comes up with a reporting API for Drupal. If you need to do something special with the data you could always write your own module to analyze it, or use some 3rd party reporting software like Crystal or Jasper to generate reports from the referralsources table.