Is it SPAM? Finding the line

Most of us are shameless self-promoters -- it's the nature of what we do. We wouldn't be publishing our own work on the Web if we didn't want people to read it, and people aren't going to read it unless we tell them about it.
But in the process of trying to tell people about our work, it's very easy to cross the line and end up angering the people we're trying to enlist as readers. And that's bad for business.
So the question becomes: When does harmless self-promotion turn into SPAM?
