A while ago we were charged with the task of using drupal with SugarCRM. Unlike CiviCRM, these 2 systems have never been designed to work together nicely. Rather than hack into core code to share a user table we decided to take advantage of the existing SOAP functionality that SugarCRM affords us.
Unfortunately we had to alter about 2 lines of SugarCRM's core code to get this to work. Also I don't think the code is as secure as we would like it. There is a point at which the password is sent (although encrypted) via a GET request. This would not be our preferred choice.