Another great Mind Meld from SFSignal. I'm not in "Today's SF Authors Define Science Fiction (Part 1)", but you know it's a topic near and dear to me. Best answers this time out are by Matthew Jarpe, Chris Roberson, Adam Roberts, and Paul Di Filippo. By "best" I mean most useful, to me, in my subjective opinion and for my own purposes in articulating why I work in this field and not in the mystery/thriller genre or something else. Which is not to disagree with those who describe SF as a marketing category, or a nonexistent territory, or a set of fun props. Because, as John Scalzi points out, it is all those things too, and rises above them on a case by case basis solely on the skill level and intent of its practitioner.
You can probably guess how I feel about this, "There's nothing special about science fiction, just as there's nothing special about any other movement or genre out there." But I'm working on both a talk I have to give at the end of this month on this very topic, AND the introduction for Fast Forward 2, so I'll save my response/energy for those.