Just rebuit cups-1.6.4 and it said this: * Messages for package net-print/cups-1.6.4: * Your usb printers will be managed via libusb. In this case, * cups-1.6.4 requires the USB_PRINTER support disabled. * Please disable it: * CONFIG_USB_PRINTER=n * in /usr/src/linux/.config or * Device Drivers ---> * USB support ---> * [ ] USB Printer support * Alternatively, just disable the usb useflag for cups (your printer will still work). I don't think this is true anymore, USB_PRINTER and libusb can coexist. Cannot find/remember where I read this although a quick google search turned up http://www.linuxfromscratch.org/blfs/view/svn/pst/cups.html
Confirming this is true. For upstream info look here: http://cups.org/str.php?L4128
There's a report of someone still having problems at the end of the upstream report. So I've kept the warning, but toned it down a lot...