Certainly a nice way to follow HN, the only advantage with the website, it to have gray links on already visited links. That's mainly why I don't use it anymore.
A "solution" to this could be a small local cache or sqlite db. Say you use Chrome, then you could have a cronjob which checks your history (given you're not in cognito) sqlite db for links in your last `$ hackernews` run. Not saying it's an adequate way to solve it, but it certainly is a hack ;)