Science fiction is a form of fiction which deals principally with the impact of imagined science and/or technology upon society or individuals.
The slashdot article and discussion Slashdot | Is Science Fiction About The Future Anymore? has touched on something that has bothered me for a few years now.
The job of SF is to ask "what if", and examine the effects. It's a way of auditioning scientific priorities socially. Remove the science and you just have fiction.
To too many, sci-fi is just a setting for a story: in the future, maybe traveling in space, lots of "computers". Sadly, this is the prevailing attitude for nearly all SF writers anymore (certainly all "mainstream" "entertainment", including Star Trek).
<rant>This attitude infuriates me for two reasons: First, it is anti-intellectual to regard the whole of science; all mathematics, physics, information theory, sociology, cosmology, ...; as a minor implementation detail. Second, it lulls the general populous into thinking that science is "indistinguishable from magic": utterly unknowable, unapproachable, fearsome, and cannot be trusted.