As a blogger, I regularly post things on HN if I feel that they will be interesting to the community here. I also often post things into the appropriate subreddit. I tend to ignore digg, and submit some things to Slashdot.
Ultimately, that works very well for technology-related articles, because all those communities are technology-minded. So, for example, when writing blog articles on Woobius Scribbles (my company's blog), if they're relevant, I'll post them here.
However, the market for Woobius is architects and the construction industry. That's a very different niche from HN. And yet, there are quite a few people linked to the construction industry on this site, as witnessed by the comments on http://news.ycombinator.com/item?id=479749 .
So, my open questions to HN users who have blogs (or read blogs) in niches other than this one are:
Where do you go to find those non-technology blogs?
Where do you go to promote your blog(s)/businesses in non-technology niches?
What are the other "niche HN's" out there?
Thanks!
Google for keywords of interest to you, talk to people in your market, talk to your customers, etc.
Where do you go to promote your blog(s)/businesses in non-technology niches?
The succinct answer: You use it to promote other people.
The longer one: blogging other people's stuff and commenting on their blogs gives you a relationship with them. Once you have a relationship with them, and they trust you, it isn't "promoting your stuff" so much as it is sharing something that they think their readers will enjoy.
Additionally, after you have a loyal fanbase, you will probably find that your most successful "promotion" efforts are a result of pulling rather than pushing. i.e. a portion of your readers who are more dedicated and savvier will take it upon themselves to spread your stuff elsewhere.
[Edit: I don't make any money off the following recommendation, and only am mentioning it because its exactly responsive to your query: I wrote a chapter in a book called BlogBlazers about this. Its the above two paragraphs at chapter length, essentially. Aaron Wall's chapter is good, too.]