If it's on topic, adds value, and isn't simply spam, then often yes, it's OK. Many readers, perhaps most readers, don't notice whether something is self-linked.

But if someone consistently self-links, and the lunk-to items are of marginal, or zero, value, then people start to notice and the person in question loses face, karma, and possibly good-will.

So, it depends.

This is, I assume the rule of thumb with anything on HN.

"Is it OK to type a comment?" "If it adds value, yes" etc.

The question that's becoming more relevant is "Value to whom?" With the increase in participants, the HN focus is diluting and widening. It seems to some that the topics on the front page are no longer as niche as they once were. It's claimed that they used to be more tightly focussed on topics of interest to hackers more than non-hackers, and that now the emphasis on being targetted at hackers is dying.

But still, "I can't define it but I know it when I see it." I still upvote strongly technical, hackerish articles, or articles that I think wouldn't appeal to a general audience, if they "add value."

In this case I personally think it's fine -- Franz is just linking to a piece written by him, which to me is like linking your own blog post. We see that fairly frequently I'd say...and SEO is of relevance to most people here (I would think). A shameless self-promo piece might find a more negative reception here.