Looks interesting, but a couple of things that jump out at me. First, the drop down "About/Guidelines" section at the top is a little crazy. Personally I would go with a landing page that describes the app, let the person enter their username on the landing page, and then move to the search feature. If I had not been forced to read the about section drop down I would not know what it was at first glance.

Second gripe is that drop down area has a horizontal scroll bar on it and I have a 27" monitor. It makes it seem as if there is content if I scroll to the right, but there is nothing there.

Finally, I am going to assume the results are tags with the various usernames underneath the tags. Personally I would prefer to tag specific posts within HN and then be able to search that. If I am searching for a similar interest I want to be directed to the specific post(s) that relate to what I am searching for. I don't want to get a username and then have to sort through their posts to find one that may relate to what I am searching for.

Overall I like the idea of being able to tag keywords within HN.