As someone with not such a Karma rating yet, I find it difficult to get feedback from HN. You only show up for 30 minutes up to two hours (depends on when you post) on the new posts list and then you vanish forever. You should not repost, obviously, so you can't do much to get your project back on HN for a while. Of course, if you know the right people, they write a blog post about you, which brings you back on HN and you'll be overwhelmed with feedback, but this is rather the exception than the rule.

Generally, it is really hard to get people to send you feedback, especially if your project/startup/tool is intended for not tech-savvy users. There will be some users giving you feedback all the time (powerusers/early adopters) and you should stay in contact even if you don't have something new at the moment

What I found to be useful is displaying a "1 minute of your time to improve the product"-form on the (in this case) applications home page, where every user will go. It is important to add a "no, I don't want to do this"-option, because you don't want to nag your users with a always displaying form-link. Don't do popups, too, they are irritating. Just a small but visible link with a do or don't option and if the user don't want to do it, don't force them again. On my last project, I got almost 20% of the user base to fill out the form this way, which I think is a really strong base for analysing and improving your application/startup/tool.