… but I gave up waiting and designed a one-sided board around the AT90USB162 in the TQFP package.
It has a USB “mini B” connector, two buttons (reset and PD7/HWB bootloader), a 6-pin ICP header, 5 LEDs (4 software controlled, 1 power), and 16 I/Os paired with grounds on a .100", 16x2 connector. Overall board size is about 2.2"x1.3".
There are several jumper wires, but they are only required if the ICP header is to be used. It is possible to use this board without the jumpers, since the chip comes preloaded with a USB bootloader.
I haven’t used the board in a project yet (In fact the board is not completely soldered) but it does work to upload firmware and control an LED. Next I’ll play with the USB personalities in the [MyUSB project
Compared to the atmega168 frequently seen on arduinos, the main drawback of the at90usb162 seems to be the lack of an ADC system.
In a second revision I’d make sure the bypass caps were properly sized and placed; they were an afterthought and I just added them where they fit. In a double-sided design I would be able to avoid placing traces under the USB; this placement is not allowed by the connector’s d’sheet pdf.
Milled circuit board overlaid with eagle board (drc 10/10):