and if oil run's low then i think you'd be more worried about what's going to heat the water in the pipe's than the pipes themselves.
IN MY OPINION:
For people with limited soldering skills plastic is an ideal way of doing it yourself providing you have the knowledge to do the job in the first place. (not saying everyone who uses's it can't solder)
I don't like the look of the bulky plastic fitting's or the way you can't run it as neatly for surface pipework say rigid copper. Underfloor, no issues.
Rat's can knaw through plastic, where as copper as far as i'm aware, they cannot (unless they had a pack of steriod's the night before)
Depending what kind of heating system you have, you may need 'barrier' plastic pipe for central heating system's as the non barrier stuff can pull in air through it's wall and cause problem's.
Hep2o is commonly available and as 'softus' pointed out to me the other day, now comes with a 50 year guarantee.
Either or, both acceptable way's
HTH Sam
(prepare's for some kind of comeback off the above comments)