This place is becoming as much of a dumping ground for vanity blogging as LinkedIn already is. There's no discouragement of accounts like this that have no activity here but self promotion.
On-Topic: Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity.
Please don't use HN primarily for promotion. It's ok to post your own stuff part of the time, but the primary use of the site should be for curiosity.
Thanks for the extract. I feel quite comfortable that my post is on-topic and gratifying. I understand others may disagree (and do in nearly every post on HN)