Author without institutional or professional affiliation Here is the case: An author has made substantial contribution while not been related to any institutional or professional  affiliation.

The question I sent to Nature:

An author has made substantial contribution while not been related
to any institutional or professional  affiliation.

Is it okay for this author to include his personal email and postal
address as his affiliation in the manuscript?


Nature answer:


  Thank you for your email. At this stage, please just include the
  author and mention this in your cover letter so that the editor is
  aware of the situation.


The question I sent to PLOS ONE:

According to your submission guidelines "Each author on the list 
must have an affiliation". However an author has made substantial     
contribution while not been related to any institutional or
professional affiliation.

Is it okay to include "Independent Researcher" as an afilliation
in this case?

If not, what is the recommended Affiliation for this Author?


PLOS ONE answer:


  Thank you for getting in touch and for your interest in submitting your
  work to PLOS ONE.
  
  Your suggestion of recording the author as an "Independent Researcher"
  for their affiliation is acceptable.  May I ask you to clarify in the
  cover letter if this co-author is self employed (i.e. charges for
  their advise/service) when submitting your work.
  
  If you have any further questions, please do not hesitate to contact
  us again.


Any thoughts and previous experience with something like this is greatly appreciated.

Thank you!
This is an unusual situation, but when it arises giving your personal address as the "affiliation" is an acceptable approach. (Whether you will get a different reaction from journals and reviewers after doing so is another question...). Note that many journals still refer to this field as the "address" rather than "affiliation", which answers the question for you ;-)

I've seen personal addresses used in papers several times in various fields; most frequently in avian ecology, a field with a strong tradition of independent local researchers. However, it crops up in various places to a smaller degree.

In some cases, I know it's a retired academic continuing to publish (without an "emeritus" status) while in others it's almost certainly "spare time"-type research. I can't speak to how common it is outside the sciences, but I've seen a number of history papers with what are almost certainly personal addresses on them, so it's certainly a known practice there.