> From what I remember, most problems with windmills are due to 2 factors: Not enough wind Too much wind

That's very apt :)

> I believe the generating curve is exponential

It goes up with the cube of the windspeed

Most windmills nowadays (the grid connected ones anyways) are of the variable pitch type, which means they can run constant RPM up to a maximum windspeed at which they are shut down to avoid damage. Such high winds occur relatively infrequently though.

Freewheeling in a storm is not an option, a windmill that runs unloaded will quickly overspeed and fly apart.