That makes sense. So far, most of the recent interviews I've had have asked me about my work experience, and none of my open-source work, even though that work is on my CV.
I did a brief screencast of something I'd built, and showed it on my tablet during an interview, which was well received although it was not a technical interview.
No, that is absolutely not a problem. If an interviewer is interested in your OSS contributions, hes's not going to be any less impressed because it's a project he's never heard of.
The simple fact that you have OSS on your resume makes you stand out. Period. I have seen exactly one resume with OSS on it in all the years I conducted interviews.
That's actually quite encouraging, so thank you. I've been trying to find a balance between working on OSS contributions + getting better at "CS fundamentals" (I'm a self-taught programmer, so a bit lacking on the algs/data structures side of things). Which is definitely a disadvantage during an interview, and part of the reason I'm hoping to emphasize my OSS contributions more.