"Science fiction is rather unique in being a type of literature that comes with its own expiration date. Of course, writing far-future fiction doesn't necessarily protect you since the next edition of Nature could knock the pins from beneath any speculative science you might be using."

-- of course, that doesn't apply to Alternate History, or to time-travel into the past. Which together describe most of my work... 8-).

Even time-travel into the future can finesse the obsolescence problem, if you're careful; the late Poul Anderson did a fine job on that with his Time Patrol series, particularly the later ones.

One should also try to avoid giving too much technobabble on how the "magical black box" works, as was common in the Gernsbackian era. After all, if we really knew how things work we'd be applying for patents, not writing fiction.