I refer to myself as a fag all the time, partly as word reclaimation- charging it with pride instead of shame- and partly because given the choice between gay, homo, queer or fag as a monicker, gay seems so common and 'happy,' homo's too reminiscient of a medical diagnosis, queer is so broad that any old softcore person who's willing to confess to a homoerotic dream can use it, but fag has a directness and an aggression to it (even 'reclaimed') that feels fitting to me. I've got a couple of t-shirts with it in huge block letters across the chest and when I wear them I feel like I'm slapping every complacent heterosexist that walks by.
As for calling others fag, I sometimes call a couple of my straight roommates/friends fags for comic effect (considering the source), and I mostly only call gay friends fag when they're being hysterical and stupid, whining and carrying on about how the latest fling that everyone warned them about cheated on them or how their erratic, borderline-retarded behaviour has landed them in some situation they don't like. Then I use it in the fine tradition of Larry Kramer, a la "god, shut up, faggot" or "wake up, faggot" because all *too* often they'll blame their hardships on being gay and therefore so disadvantaged instead of taking responsibility for their behaviour. And mostly, those are the friends who are so used to *everything* being 'gay' this and 'gay' that, gay being the bricks and mortar that make up their whole world and so ubiquitous that it acts like a smokescreen or a shield they hide behind and blame everything on, so when you smack them across the face with "faggot" it gets their attention. Maybe because a lot of them haven't reclaimed it, and still find it offensive, but despite all their belly-aching about their 'hard' gay lives, they've never even been called a nasty gay-word to their faces.
And then there's other people calling me fag, and that's very context-sensitive. If it's a friend they usually say it like "he's our angry fag" which sits fine with me. On the other hand, if someone calls me a fag thinking that it'll hurt my feelings or give them some power over me, I disabuse them of that illusion pretty quickly. A favourite is "that's MISTER Fag to you."