I've just returned from Denver and the World Science Fiction Convention (worldcon) where I spoke on issues such as privacy, DRM and creating new intelligent beings. However, I also attended a session on "hard" science fiction, and have some thoughts to relate from it.
Defining the sub-genres of SF, or any form of literature, is a constant topic for debate. No matter where you draw the lines, authors will work to bend them as well. Many people just give up and say "Science Fiction is what I point at when I say Science Fiction."