I disagree, especially about posting comments. When I was running my social "cute" site, I hired my niece to post comments on icanhazcheezburger, and to have cuuute.com in the sig (the site is dead now). I routinely got 2-5 clicks a day from people clicking through her sig.

And, pretty routinely, every time I post a link to my economic social news site, http://newsley.com. I get around 70 clicks. Frankly, the people that come to Newsley from HN give me the best feedback and are my best users. In fact, a large portion of my first 1000 visitors came from HN. I get a lot of bounces, but i also pick up a couple of regular users every time. Granted, the demographic that I'm looking for actually intersects with HN's demographic somewhat.

I can also vouch for leaving links in the body of comments. As long as your link is on topic to the blog post, I really don't have any problem at all dropping a link in a blog comment. I think it can often add to the discussion.