Just thought to let people here now that I have created a four-part tutorial that starts from very basics (soldering a USB cable to a pin header) and goes on to explain V-USB usage on ATtiny2313 device (should work for most 8-bit AVRs with a little tweaking):
http://codeandlife.com/2012/01/22/avr-attiny-usb-tutorial-part-1/ (USB basics)
http://codeandlife.com/2012/01/25/avr-attiny-usb-tutorial-part-2/ (complete sample circuit on a breadboard)
http://codeandlife.com/2012/01/29/avr-attiny-usb-tutorial-part-3/ (firmware with V-USB and PC side with libusb-win32)
http://codeandlife.com/2012/02/04/avr-attiny-usb-tutorial-part-4/ (transferring buffered data between device and PC)
Hope this helps someone. And thanks for obdev guys for a wonderful library!