strykeroz:
fungus:
There's a hardware limitation: Pin 3 can only output the inverse of pin 4, pin 4 is the 'true' signal.While that's strictly true for the datasheet, in reply #38 of this thread on ATTiny85 and PWM Coding Badly explained that the inverted PWM output can't be used by the Arduino cores for ATTiny. My own testing confirms this gotcha - that D3 is not able to use hardware PWM with the arduino-tiny core. Software PWM like the tone() function works fine on all 5 of the standard ATTiny85 IO pins though, so there's an easy way around this limitation if you must use that leg.
I don't know how the cores use the timers. I know that using hardware PWM on D3 and D4 at the same time wouldn't work for analogueWrite() functions.