To test the circuit I used the HID mouse wiggling example from http://codeandlife.com/2012/02/11/v-usb-tutorial-continued-hid-mouse/ . I've had troubles with enumeration before with V-USB and ATTiny85 but having the 3.6V zener diodes seems to mitigate that -- it enumerated on the first try.

I also ran a non-USB color fading test with pleasant results