Consider this response to a question I posted back in October.
My question was answered within days, I accepted the answer, and the accepted answer has been upvoted significantly.
What to do when someone posts a link their own blog, where the subject of that blog essentially is the answer that was accepted months ago?
Ignore it? Vote it down? It is a kind of self-promotion, although clearly his answer is on topic and correct, but it was unnecessary owing to a very widely accepted response.
This is an interesting question. There is nothing wrong with linking to another site, answering a question that already has a marked answer, or even answering a question that is old, but I think if you are going to do that it should be on something that either adds to the explanation or provides a different view point.
It is also useful to provide some sort of snippet from the blog post to show that the post is relevant to the question and allow the user to decide using that small amount of information to proceed to that site. In that particular example, the user essentially answers with just a simple link with no further explanation. The post itself isn't really off topic, but it provides no additional information to the post. It would have been much more helpful if the user would have posted something along the lines of:
I wrote a blog post about this. Here is the relevant information to this question:
Some extended quote from the post
For more information, check out my blog post here
Essentially, we need to make sure that the user adds good relevant answers to this site before they look purely for the page view on their own site. There is nothing wrong with having a blog and looking to generate traffic to it, but you need to provide more in your answer to be able to just link to your site. Unfortunately, without providing more details, it is essentially spam even though it is pointing to a relevant article.
EDIT: Just wanted to take a moment to record my results here. I downvoted that particular post, linking to this article as a method for the type of thing that should be added. The user read this post and revised their answer to make it much more SFSE friendly. Because of their efforts to remedy the problem, I changed my downvote to an upvote. This process seemed to work really well.
It is a kind of self-promotion, although clearly his answer is on topic and correct, but it was unnecessary owing to a very widely accepted response.
The fact that there's a widely accepted answer doesn't necessarily mean that adding another is unnecessary as such. I can't count the number of times I've searched for a solution to a problem on SO, and found an answer that's just ever so close to solving my problem, scoot on a few answers down, and find someone who's posted 6 months later with a solution that, while very similar to the widely accepted answer, has faced exactly the problem I've faced, and provided exactly the right solution.
I wouldn't downvote personally unless it was just a link, but I most likely wouldn't upvote something posted months later on a question with an accepted answer unless the post specifically drew attention to where it differed from the accepted answer - or if it made the accepted answer more clear (I've seen plenty of accepted answers on SO that were incredibly hard to follow, which get re-hashed in a simpler fashion further on)
The initial edit of the question was nothing more than shameless self-promotion and didn't really contribute much, especially when clicking had a notice in the upper right that he's looking for work! The edited version on the other hand now includes notes about an important caveat to my answer (from 2 days before I updated my answer with a relevant link, so he clearly did his research). The redundant bits are left on his blog and not brought over to the SE answer.
As the answer stands right now I think it's a useful elaboration on my initial answer, and deserves to stay for future readers with similar but not identical issues. He clearly put in effort tailoring the current revision for SE, and it adds value.
