There have been LOTS of threads on the +'s and -'s of PTO sets.
http://www.tractorbynet.com/forums/attachments/222798-tractor-power-take-off-generator.html
http://www.tractorbynet.com/forums/attachments/222861-power-take-off-generator-one.html
http://www.tractorbynet.com/forums/attachments/215098-generator-options.html
There are four basic petroleum types for generators - Natural gas, LPG, diesel, gasoline, all readily available.
Upon review (in my memory) of what I've read here the general consensus was that a natural gas/lpg was more cost effective solution, cleaner, easier for a standby emergency generator in the 10 to 20K range.
BUT T - you need the infrastructure for nat gas/lpg.
Currently nat gas is CHEAP lpg is dear.
Nat gas is at a 10 year low:
The Associated Press: Natural gas prices stay at 10-year low
Propane follows crude oil:
Factors Affecting Propane Prices - Energy Explained, Your Guide To Understanding Energy
The infrastructure for nat gas is simple, if it already runs by your site. LNG seems rare. The infrastructure for LPG is ubiquitous, you can buy a bottle anywhere, even in a dry county.
Diesel and gasoline are dear, but almost everybody that is rural probably has at least 5 gallons sitting in their car or truck, or tractor.
So I had planned on a natural gas standby generator. But I bought a house nowhere near a natural gas line.
With the price of the remaining fuels being about the same a PTO gen set seems a clear winner for me. I'm probably going to have two tractors (seats) anyways and only have one seat (mine) to fill them. I've my infrastructure for significant diesel storage
And I anticipate requiring power at separate sites, my workshops are about 80 yards from the house and on a separate pole/meter.
So now I've another item to add to my Craigslist shopping cart.