This is great advice.
When I created http://sleepyti.me, the first place I posted it was here to HN for feedback. Using that feedback, I was able to make signficant improvements and bug fixes. Reddit's /r/web_design subreddit helped me out with the look of the page, and now my site--albeit not a startup--is earning almost enough money to pay my rent. It's not a $200M Heroku buyout, but it's not bad for a small, simple web app.
As others have said in this thread, the most important part is to genuinely want help, feedback and discussion. Don't post to HN to argue with participants, or to try to spam your link enough to get noticed. The value of the HN homepage isn't necessarily the traffic, but the feedback.