I appreciate it when the names characters use for one another have significance. They can be a shorthand for the level of intimacy, the context of the relationship, and how people see one another; they're also indicative of the culture in which these people have learned to relate to one another.
In Person of Interest, none of the relationships between the regular cast is social or familial. It's all about working relationships (or antagonism), though admittedly everyone's ideas of 'work' tend to bleed over into their personal lives. Even counting the relationships with recurring characters, very few are what you'd call normal friendships, and those mostly appear in flashbacks.
Add to that the fact that so many of our characters don't use their real names to begin with, and the results are fascinating.
So! What names do each of them choose to use for one another, and what (if anything) do you think that means? Are there situations where you think they'd use names other than the ones they use on the show? Is there a difference between canon and fanfiction? If you write fic, do you pay particular attention to this?