I think that libusb should be a requirement for hpoj. I couldn't get my USB printer up and working because I didn't have libusb installed (if you are hooking up a USB device anyway, it's a good idea to have it). See: http://article.gmane.org/gmane.linux.drivers.hpofficejet.devel/561/match=1210 for the specific issue I had (but there could be more)
will have a look .. sorry for the delay there was a problem with the mail alias so i didn't get the Bugzilla mails
fixed, see attachement to bug 21108
added usb useflag