We don't get them often -- usually a couple a year for an hour and a half or so (typical scenario something breaks and it takes them an hour and a half to fix it), or after a big storm (maybe once a year on average) where it can be off for several hours. I'm always mindful though (especially after seeing what happened in Christchurce after the quakes), that what's happened in the past is no indicator of what may happen in the future -- in their case many thousands were without power for several weeks, and in that situation, having portable generators would make a HUGE difference to quality of life.
Having just said all that though, they're also a god-send for using studio strobes in the field (each one can run 2 lights), but they're also useful for hair driers / hair straighteners / hair curlers / fog machines etc.