In a beta report thread, Wheeloffire says: "Science fiction isn't about the future. It's about now."
I most unhumbly disagree: it's about both, and more. While I very much enjoy the "realism" in most any sort of fiction, what sets SF apart is that the good stuff makes you think *beyond* the here and now. Sometimes that means hardware stuff that sets engineers to scheming, and other times it is "soft" stuff that sets folks to imagining themselves or their societies with fundamentally different values, fears, and aspirations.
Samuel R. Delaney wrote a great essay on what SF is (no SciFi for him, too limiting) and I'm too sloppy to remember the name. But he had a pretty simple argument for what makes strong SF: evocative phrases like when Heinlein first wrote "the door dilated open." Great 4X space games combine a practical (better word than realistic, IMO) modeling system with an engaging narrative layer that sets at least part of the audience off on their own imaginitive trails. Arguing over "realism" is just one of the kinds of fun in SF land.