Great Concept, Needs Some Refinement
I found that the Drupal Invite Module is a great start in the right direction for such a project. However, I also discovered that there are a couple key features that would be nice for them to work on.
The main issue I found revolved around sending an invitation to an individual who was already a registered user. First of all, I wanted to be able to send ANYONE an invite. So, in my implementation, I removed a portion of the module code that checks to see if the email address is already in the database.
Next step is more tricky. You have the option to promote registrants to a selected role after they've accepted your invite and registered. This is great! But I also want existing users to be able to be promoted to. This feature was left to be desired. So we wrote a hack to do just this.
Other than this missing feature, however, the module is really as bundled.
Robert Nelson Vance
Owner, proVanceTek LLC