What IS Sci-Fi?

So what IS Science Fiction? We bandy the term about all the time, yet I believe it's a somewhat amorphous term we all nod our heads at and don't actually define. Sci-Fi means different things to different people; while that's as it should be it DOES make for some confusion, whether that's between author and publisher, book seller and customer, or fans.

Whenever I think of Sci-Fi, the first thing that comes to mind is advanced technology: space flight, planetary colonies, ansibles, etc. Obviously, this has to be examined relative to the time the book was written. (Very little of Jules Verne's technology is cutting edge NOW, but at the time it was written? THAT's a different story.)

Aliens also automatically mean Sci-Fi to me. Life forms from another place and drastic mutations are just as significant as spaceships in defining the genre.

Orson Scott Card, in his book How to Write Science Fiction & Fantasy, discussed several boundaries defining speculative fiction. The essence of that discussion, and the (admittedly) over-simplified definition that results, is as follows:

Science Fiction includes all stories that take place in a setting contrary to known reality while following the same rules (and logical extrapolations therefrom) as our own.

What do you think? Accurate? Weak? Too exclusive? Too inclusive? Let me know!