You can log anything you want. The issue is counting time for higher licenses or ratings, or for declaring flying time for the purposes of an aircraft insurance application.
In aircraft which are certified to be operated by a single pilot, which is essentially all non turbine GA aircraft there can only be one PIC. The only way for another person to log time on the same flight is if he or she was an instructor in which case the first person is logging dual not PIC. There are 2 general exceptions to this. The first only concerns flights for the purpose of a flight test with a designated examiner and the second is a bizarre FAA ruling which permits, under the safety pilot situation under discussion here; for both pilots to log PIC.
Pretty much every other regulator in the world thinks the idea of having 2 PIC's is stupid and won't allow you to count any of this time towards higher licenses or ratings.
The "safety" pilot function is solely to keep a good visual look out. Other then that you are passenger. IMO and what I believe is the official explanation for not allowing the time to count, is that you are not performing the majority of the actions inherent in piloting an aircraft and so that time should not count anymore then occupying seat 34B on the Boeing going to a Spain for a piss up with the boys.
However like I said you can log anything you want just make sure that your log book entry accurately reflects your duties and I strongly advise that the time should be written in a separate column so that there is no way any regulator can think you are trying to pull a fast one. IMO your chance of getting any regulator, other then the FAA, to count safety pilot time towards a higher license is zero.
Last edited by Big Pistons Forever; 24th October 2012 at 16:57.