Drupal extension is a set of Core API extensions that offers a full access for Drupal modules (magento_* that can be downloaded here : ....) to Orders, Catalog and so on.
This extension, will offer you to TOTALLY bypass Magento front office, using Drupal instead.
When a new user is created a Magento user is automatically created also.
Orders can be created from Drupal, cart is managed from Drupal.
Catalog is syncrhonized, so each Magento Product is a Drupal node that you can push into Views, etc....
We're actually porting some paiement gateways (Paypal) so paiement process remains in Drupal also.