I've interacted with at least three Caravel users at GC who needed to upload files who somehow made it to the File Manager, and saw the text "Upload files", but then had no clue what to do next.
I suspect that the "Upload files" link is taken to be non-link text: Unless the mouse is actually over the text, the typography is identical to "Folders" and "Information" on the same page which are not links.
My suggestions (in order of preference):
* Create an "upload" icon and put it in the icon bar at the top of the file manager.
* Do away with the "gray bar" at the bottom of the file listing, and use something that looks like a button in the whitespace below the file listing.
* Make the link visually more like a button, and place it below the gray bar at the bottom of the file list.
I suspect that people are also overlooking the "Clipboard" link towards the bottom of the File Manager.