I wrote a simple referral module without looking too much at the affiliates module. I know my module is not as sophisticated as that module but it is Ubercart v2 and drupal v6 compatible (I'm not sure if the affiliates module has been ported, v2 still lists as Ubercart v1). You create a referral account and get provided a link. Then track referrals in the reports section. This is also a beta release that requires formal testing.
UPDATE: starting with beta 3 you can associate referral accounts with Drupal accounts and the Drupal user can review a summary for their referral accounts.
Extract and copy to /sites/all/modules/ or /sites/all/modules/ubercart/. Then install under modules section. Grant the "configure referrals" permission to the proper roles. The module adds a menu item under "Store administration"/Configuration, and a Reports menu item.
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