Two recent comments here at the Orb that I chose not to publish. So here's my thing on that:
If you leave a comment with a link to your site asking me to link to yours that's spam. Maybe not truly, technically spam and the intentions might be innocent, but it's still spammy, even while being naive.
The second post was a negative and sarcastic one-liner about someone's article. If you have something constructive to say: reasons why you don't like something, something to contribute, fine. But a throw away smarmy comment that isn't productive -- I won't publish it. Serves no purpose.