Neighbor has a whole house natural gas generator and loves it. The funny part I would say in the last five years it was needed maybe twice for a total of a couple hours.
A relative of mine has one for his beach house I haven't spoken to him today but IIRC during Irene it got flooded so it didn't help him
http://www.amazon.com/gp/offer-listing/B004E2GCFC/ref=sr_1_2_olp?s=office-products&ie=UTF8&qid=1351635255&sr=1-2&keywords=APC%C2%AE+-+Back-UPS+Pro+1000+Battery+Backup+System%2C+1000+VA%2C&condition=newi have one on freezer / fridge
4) natural gas has its positives- but if the electricity goes down- how do you know the gas won't either?
2) A portable generator will need to be refueled every couple of hours. With a built in generator, its normally attached to your gas line and you don't need to worry about refueling.
I would add - that in cases of 2-3 day power outages gas stations are likely to have also lost power and you will need gas for the generator... Also running on natural gas is much cheaper that regular gas.
They do sell portable generators that run on natural gas or propane too.
How would that work?They make small (<10k watts) with a port for a natural gas line?