The first post I submitted was a most-mortem about my startup. IIRC, it make the top 5 briefly. The doors opened to me because of that were shocking. I had many job offers, phone conversations with a few well-known tech personalities, and tons of traffic.
At the time, I felt the comments on HN were extremely negative. But, many opportunities and contacts arose from that thread outside of HN.
Later, someone posted my new ebook landing page to HN. The ensuing traffic built up my email newsletter and is still one of the main sources for my sales. Again, the comments on HN were very negative, but I met lots of positive, supportive, excited folks when they signed up to my newsletter or followed me on twitter. All because they found me on HN.
From these experiences, here's what I've learned about HN. It might not be very surprising:
-There is a very negative and very vocal minority that comments actively.
-There are many more positive, helpful people lurking. (If you can find them.)
-If you post your project to HN, you better have thick skin.
-HN is not only a great source for news, it's a powerful resource for founders.
-Because of all the strange and hidden rules about up-voting, getting your project in front of people on HN is all about luck. It has nothing to do with you.
*edited for bullet point fail.