It's possible to have a nice launch at HN, but whether or not that's going to translate into much value is another question. If you have a really great product that everyone just loves, and it's free (or free to try), and it's built for viral growth - then getting to the top spot at HN might jump start things for you.

But to anyone who doesn't manage to get any traction on HN or PH, I wouldn't worry about it too much - it's one of those things that's nice if it happens but you shouldn't be counting on it in your business plan.