A post from "the other side of the table" :). The previous company I worked at, I hired two people through who's hiring posts. We pretty much tried it out for about six months as we didn't have much luck through the more traditional channels our division's HR department used. So yes, there are real positions being filled through these posts. That said, just because it's on Hacker News and this is an informal place do…
On the applying side, I choose only 5 companies last time and wrote very strong cover letters. Got a call from all of them. HUGE time saver when job searching, be picky with who you apply to and craft a good cover letter.