Jason,
Like Steve said, the key to engine use is how it is used. If you are going to use the engine under a load at operating temperature (driving), that will be beneficial, but cranking up the engine and letting it idle is not. So unless you are going somewhere, starting it and letting it idle is not advisable. The same thing goes for your generator, if you are going to "exercise it", run it under a load by turning on A/C units or electric heaters depending on the weather, because you are not only heating up the generator engine but you also heating up the generator section to avoid moisture problems.
Gerald