I had a similar experience. I just left ClearChannel last month to go work at a startup, and though I went through a recruiter to find my new job, I also applied to a handful of job postings at YC-funded startups (through the jobs link at the top of HN). I believe there were 5 total, and 2 of them had puzzles that I completed correctly. I have an impressive resume, and I was willing to relocate (I live in Los Angeles, so SF isn't too big a change). Not one response, even to say we got your email, thanks for doing the puzzle. Through the recruiter, I was interviewed and hired within a week, at a 37.5% salary increase. Go figure