With respect to speed governors, on my utility-parallel setup, it's not an issue since the utility controls the frequency. All the governor does at that point is maintain the power output at the set point. If the utility disconnects, then the speed governor "catches" the engine as it speeds up after being suddenly unloaded.
For the grid-independent folks, the mechanical governor on the Listeroids does an amazingly good job of speed regulation, considering how crude it is. If someone needs dead-accurate frequency control, we can fix them up with an electronic governor. These are made by Woodward, Governors America, and Synchro-Start. There used to be another company, Barber-Colman, but they were bought by Woodward. The system has three components, a speed sensor, throttle servo ("actuator") and the governor ("brain"). It'd require mounting a ring gear somewhere so there are gear teeth for the magnetic speed pickup to sense, but it could give very accurate speed control from zero to full load ("isochronous governing"). The cost for the whole setup would approach $1,000.
Frankly, I doubt anyone on this forum really needs that level of accuracy on their frequency control. Just don't run your alarm clock on the Listeroid.
J.S.
Highland Power