I recently came across an article about 16 Different Clones you can Build with Drupal. I have seen most of the clones on the list such as Digg clones and Facebook clones. The one clone that I have not seen is a file management web site clone. In the past we have built a lot of projects using Amazon S3 and the Media Mover module mentions in the post. We have however only used that for basic document management to support content editing, as oppose to building a complete site like Box.net. This article reminds me of a recent email discussion in the IT mailing list of the University of Chicago where there is a question about a Drupal theme to build a file management site. Back then the discussion pointed towards using Alfresco as the document manager.
Looking at it now, and having been exposed to both Alfresco and Drupal (we provide services in both platforms), I would still say that Alfresco is a better document manager. I see Drupal as a great web content management, however, when we start talking about repositories and file folder structures, Alfresco remains to be more superior. As an example, it will be quite a bit of work to set up a shared drive in Drupal with a complete interface. I think that part of this is that both systems have a different focus. Drupal started as and has always been a web site management tool. This includes intranets and extranets. Alfresco started as a competitors of Documentatum which is primarily used internally by staff members. While all of these systems can support web sites, Drupal is the one that is dedicated for it.