It's well established that answering your own question is a good thing.
But can you have too much of a good thing? I just came across this user - 21 questions, 12 of which are self-answered (not always self-accepted).
What's the consensus on this?
This user is behaving the way we want users to behave.
On the questions that I saw, when he answered the question himself, he wasn't stealing from answers that other people posted, he was posting a completely separate and unique answer, because the answers provided to him did not solve the issue.
This is the perfect behaviour because the issue is solved, and there is an accepted and correct answer so that other users can find it if they have similar issues.
I don't see it as a problem. You will only get up-voted if your answers are good, and you won't get anything from accepting your own answers. If you're clearly gaming, I think you'll be met with a slew of downvotes. Answering your own questions increases the risk of getting more-than-average downvotes. There's really more risk than gain in this - if people want to do it, that's fine, it's their rep that is at risk if they do it wrong.
It's great to post a good question and an answer you know to build up a repository of solutions. I hope one day to not have to search anywhere else on the web for the answers I need.
I think there are a good amount of questions where if you can anwer them yourself they don't deserve asking.
Answering your own questions should be the exception not the usual thing to do.
If you can find the anwer after 5 min. yourself, then why bother asking in the fist place, it's against the point of an Q&A site.
You ask when you don't know or are unable to find the answer with some effort, else you're filling the site with noize and low value questions.