Many small businesses would prefer to let their server drop on power failure than to pay even $100 for a cheap UPS. It's often difficult to convince them of the value of something like that; it's why they like ESXi. It's free, they can save a lot of cash by putting a bunch of linux servers on one machine, and then I get paid. :)

If the ESXi server experiences a power outage, it is set to come back on automatically when power is restored. What happens with the guest OS's? Ideally I would like them to all come online again as well, assuming they were on when power was lost, but I see no option for choosing this.

I don't want to yank power to the system just to try it out, of course. I'm sure someone knows what happens by default, and perhaps how to make my system to work as I would wish.