yeah, me too. It's funny though...I was listening to Neal Stephenson's seminar "Sci-Fi as a literary genre" (easily found by google) where he preferred the broad term of speculative fiction - basically *anything* that's essentially sepeculative/out-of-the-ordinary. 300 the movie was spec fic to him.
There was a funny anecdote where a friend of his (bruce sterling?) defined a thriller as an "SF novel that includes the President of the United States" - I lmoa'd on that one.
But i've been struggling to define more specific categories just for myself - I tend read everything between scifi and fantasy...and I like to categorize things.
Lately I've been reading H.P lovecraft short stories - of whom i've never read before.
First, it's amazing how much science is mixed directly with the paranormal - for ex, Beyond the Wall of Sleep.
Second, it's interesting to note that Lovecraft's style is, I think, what some would classify as "telling, not showing." But he does it well.
Very instructive...
On that link above I plan on reading Benford's novel "Matter's End" next.