Someone built a board that uses the ease of programming of Arduino software with a PIC microcontroller. And it uses 18F2550 that has a built in USB and
a hardware serial port. Linux, Mac, Windows are all supported, the sketches work like on a regular Arduino board (almost, there are some hardware differences). Open hardware and software, as usual. Robopinguino anyone?
Here's the link:http://www.hackinglab.org/pinguino/index_pinguino.html