Currently, the only ways of getting content and metadata into the system in bulk is to use the ACP import format (XML + content) or the APIs. The PHP API might provide a quick way to write some directory scanning code with inserts to Alfresco.
The ACP import needs you to create an xml file with the metadata you want to import - it's a simple format, just do an export of a space to get an example. There is a Forge project that generates ACP files from a CSV file of items.
We will develop a file-system "scrapper" in the future (unless someone does it before us), but part of its purpose will be to assimilate the content in-place - e.g. not copy content.
Paul.