I have often used those three terms almost interchangeably, yes, even computer scientist. After all, most of us have a degree in computer science, so what does that make us? However, recently I find that those three things have come to take on more and more distinct personalities in my mind. It has come to the point where if I think about someone I know – or know of – within the industry, they immediately fall into one of those three categories. Which is not to say that one person can't have attributes from all three, but regardless, they always tend to favor one most strongly and so I fit them into that category, programmer, developer or computer scientist.
It is difficult to define what each one should be, (it is more of a gut feel rather than a strict delineation) they are very similar (and rightly so), but I am going to attempt to do it anyway, cause I am a glutton for punishment :).