> A. It is a matter of interpretation whether a given system can be
> described as a computer running a specified program P
This proposition is definitely false.
It is true that information content is largely observer-dependant, in the sense that I can choose any scheme I like for mapping physical phenomena to data. In this sense you could view any complex object as encoding all sorts of different programs, using many different schemes. However, this does not imply that any system can be interpreted as 'a computer running a specified program P'.
The problem lies in the fact that a computer is not a static body of data. One could view your couch as encoding a complete blueprint for my computer, but that is not the same thing as actually being one. To qualify as actually being a computer, your couch must display a certain range of behaviors in response to environmental stimuli. It has to maintain an ongoing chain of appropriate, causally connected states while running a program. The thermal vibrations in your couch are never going to display this behavior, no matter what encoding scheme you use.
Billy Brown, MCSE+I