I think seansean8 has a very good point, document repositories should be able to allow filtering of documents by metadata, such as categories or tags. I did not find this yet in Alfresco, and it surprises me since that is the first thing that would be needed, from a users perspective. Nowadays the use of folders is old fashioned and limited, since you can't assign a document do different folders at the same time without duplicating the document. Filtering is the first feature required when organizing and working with files and documents in an enterprise enviroment.
If such feature is already present as plugin, please let me know
Thanks