I wonder if there is a project were you can burn the Arduino Bootloader to a different AVR microcontroller USB capable.
There are several projects that use the Arduino bootloader on different more powerfull AVRs than the 328, like Sanguino (http://sanguino.cc/) that uses a atmega644p, but i cant find anything on a USB capable AVR.
On the Arduino UNO board we find an atmega16u (http://docs-europe.electrocomponents.com/webdocs/0eee/0900766b80eee730.pdf), acting as USB-to-TTL interface, since is a USB capable AVR, why the arduino (even the DUE version) does not come with a USB ready AVR???? Microchip and the same Atmel has plenty of microcontroller ready for USB.