I setup a USB drive last night following the wiki post.  I was able to connect to the drive, but I did not have permissions in order to create a new directory.  There is no setting in the web UI for permissions, but I found a reference to where to change this in the OpenWRT interface.  I tried changing this to read only, and back to read and write, but this did not correct the issue.  Are there any suggestions on what to try next?