Sta-Bil additive is every piece of power equipment I've got, there isn't anything better for engines that get intermittant use. Even draining the gas for storage doesn't totally remove it from every passage in the carb, and that's were gunk will form and ruin your day, Sta-Bil prevents that.
Almost every Spring when the bikes come out, I see someone on the side of the road with engine trouble and that old ad pops in my head, "SHOULD HAVE USED STA-BIL!".
Here's a link:
http://www.goldeagle.com/sta-bil/
Agreed, natural gas is great for back-up, but 95% of the generators sold run on pump gas.