This is a topic that's been brought up a little here and there, but not something we've gone into very formally yet. Specifically, this was prompted by this post today. Not to pick on @nkv too much, but it makes a good example of a user that (so far, at least) has very little activity outside of posting about their own project/business.
For my personal opinion, when I was a moderator on reddit, the guideline that I would generally use to explain to people that were overly self-promoting was along the lines of: "It's fine to be a redditor with a website, but not a website with a reddit account." When I started working at reddit later, this was included in the "Guidelines for self-promotion on reddit" wiki page (though some Confucius guy stole my credit).
Reddit doesn't follow those guidelines any more, but I've always thought it was a reasonable way to explain the distinction. Members of the community occasionally posting about their own projects is good (and something we should want to encourage), but we don't want people outside the community coming and trying to just use established communities as a source of traffic.
What are your thoughts about self-promotion in general? How should we try to determine if someone's activity on the site goes too far into self-promotion territory? If we find people that are over that line, how should it be dealt with?