I've been working on a module for sometime that uses Authorize ARB and deals with role promotion:

http://drupal.org/project/role_subscription

I decided to build it outside the scope of ubercart initially bc I thought recurring billing (not invoicing) wouldn't integrate well with ubercart which essentially deals with single payments (and recurring payments).

Anywho I suppose I'm wrong bc I see Authorize ARB integration and recurring billing in Ubercart, now I'm thinking I may need to rethink this bc if all I need to worry ab is role promotion then maybe that's the way I want to go as Ubercart is much more feature rich and better supported than my more barebones recurring billing module.