its really amazing that USB with AVR is simpler than RS232C -
RS232C needs proper level converter, and USB needs one 1.5K resistor !!!
Just checked the "IgorUSBPlug" - total 4 components
2) 12MHz crystal (no caps !)
3) 1.5K resistor
4) 0.1uF VCC filter capacitor
thats all, the above does enumerate and work as USB device!
trying the same with RS232 more components are needed.
just a notice, maybe not all of the AVRfreaks are not yet aware
how easy USB is with AVR - with non-USB AVR !!!