Hard as nails?

I'm a voracious reader. I usually have two books on the go. One, I read on the train when going to or from work. The other, I read at home.
Generally, I read SF. I'm currently reading Black Man by Richard Morgan at home and Eos's The New Space Opera (a collection of short stories) on the train. I'm struggling a little with the former (what with the demands of an 8-hour working day plus two hours of commuting, plus all the other things wanting my time), but I am really enjoying the latter.
Space opera is a funny thing. The space operas I read when I was younger included such things as Asimov's Foundation Series, and E E Smith's Triplanetary. They showed their pulp-magazine origins, not being especially scientifically rigorous. Space travel was achieved through such literary conventions as hyperspace or warp drive. TV series such as Star Trek continued this.
Now, however, I think it's much more rigorous. Authors such as Peter F Hamilton, Charles Stross, Stephen Baxter and Ken Macleod have used harder science in their work, eschewing or minimising such conventions.

By comparison, an author such as Kevin J Anderson (and I'm not putting his work down, I do think it's quite enjoyable) has not taken such a rigorous route, and I think it's somewhat diminished as a result. Much of his work feels cliched, and sounds like it could have been written any time in the last fifty years or so.
Paradoxically, authors who've limited themselves to the more scientifically plausible seem to have opened up their options and produced much more imaginative work. Most notably, Alastair Reynolds' Revelation Space sequence has managed to produce a powerful and gripping space opera without faster-than-light travel at all. It's also quite a dark universe, and all the better for it. I've also found Stross's Accelerando, which also takes quite a hard-sf stance, to be a fantastically imaginative novel.
With SF, it's easy to imagine a universe without limits, and with that you just don't know where to start. I think that by limiting themselves to the more plausible scenarios, authors set themselves guidelines they can work within, thus enabling them to run much further with them.
If you're not convinced, head on over to Orion's Arm. This is a hard-sf collaborative worldbuilding and creative writing project, and one of the most imaginative things I've ever seen. You could easily spend days going through its pages.
One of the best known hard-sf writers is the venerable Arthur C. Clarke. In the intro to The Songs of Distant Earth, he described the likes of Star Trek and Star Wars as fantasy rather than SF, and I'm inclined to agree. Science fiction is based on science, not literary conventions such as hyperspace, and for me it's at its best when it remembers the science that forms its core.