Has anyone taken a look at the new Quickbooks API contrib module on d.o.?
Quickbooks Module in Drupal.org Contrib
Check out Sarva's recent Quickbooks API improvements patch (http://drupal.org/node/298079) and the new Ubercart Quickbooks Integration module (http://drupal.org/project/uc_qb) for a working solution.

I'm excited about it: http://drupal.org/node/270204
Still in correspondence w/ the author... haven't had a chance to get into coding anything, though.