Generators are likely not to be available right before a storm hits. Ownership is really the only model that works for items that are needed at exactly the same time, by everyone who would ever need them.

This is a big problem with the community sharing model. It seems like at least twice the hassle of craigslist exchanges since you have to coordinate two physical meetings rather than one. Then there's the whole issue of the borrower isn't quite done with the object yet, please try again next week.