Yeah,I got that info about the 740mL PET bottles from PB2 on the Cooper's forums. He also said the PET bottles are lined with some nylon to aid in o2 barrier protection. That's another reason hot water should never be used in them. And he also said the PET bottles are good in that regard for up to 8 months. Def not the kind of bottles for long,extended aging. But for something on the order of my Burton or Whiskely ales,they'd be fine. Those had to age about 10 weeks in the bottles for example.
I imagine this sort of thing would also go for the Better Bottle type carboys as well,since the one I have is listed on the side as PET plastic.