Primer is well known within the Science Fiction community as a classic, brilliant, film, although not everyone has seen it (you should). Yet outside of SF, in the civilian world, hardly anyone has ever heard of it. Which is criminal, because it's insanely amazing. It's like the film equivalent work out to your brain as the novel Permutation City by Greg Egan, or Back To The Future 2 to the power of 12, or a years worth of brain training on your DS.
Actually, in my experience, films like this are better known outside of SF than inside of it.
People who are into films in general are quite likely to have stumbled across an indie film as well written as Primer. Especially if it did the festival circuit.
By contrast within SF, as the Hugos show, people have little interest in anything that isn't linked to an interesting IP or marketed to within an inch of its life. Which is fair enough... Sf people tend to be into books and not films but I learn far more about cool underground genre film by reading Sight and Sound than I do from reading SFX or the blogosphere.
Interesting. Point taken. It's true that my unscientific sample of "people I know" don't include many people who follow the indie film scene. Maybe that's just another overlapping sub-genre of person and I should have been more specific: I'd count it being known by the mainstream if it gets shown on ITV :-)