Ask HN: Are job postings acceptable?

I always thought that posting job openings would not be acceptable on HN.

However there was one recently posted at http://news.ycombinator.com/item?id=476495 and nobody commented that the post was unacceptable.

I ask because I do from time to time have contract work available, but, on the other hand, we certainly don't want HN to turn into a jobs board.

Forgive me if I missed them (I did look) but are there any guidelines regarding posting jobs on HN?