I've always had trouble with that term with its implied elitism. I tend not to use it--it equates in my mind with "customer service representative" and suchlike.

But not everyone uses it that way. The people I respect who use that term tend to use it mean a combination of common sense and doing one's best.

See below for my approach to it. I think it's interesting, the attitude toward "professionalism" and a "professional organization" such as SFWA in our particular sandbox -- seems to me that the egalitarian nature of the fan/pro spectrum (many pros are unabashed fans, fans become pros, many people feel they could be pros/desire to become pros) sometimes produces a certain resentment of anything that . . . not sure how to put it . . . marks the latter group as different? That's not exactly it. I personally have no problem with a professional writers' organization establishing minimum entry requirements, but I've heard people complain about SFWA's elitism in that regard. Likewise, I see nothing elitist in the concept of professional behavior -- it's an obligation on those who wish to make a living in this field, not some kind of prize.

Ditto the ideas of "lady" and "gentleman": I dislike the elitist implications of the terms, but that doesn't stop me from using them as role models while attempting to avoid elitism in myself.