You're encouraged to do that. I wonder why it seems to upset so many people? (I'm honestly curious, I'm not trying to be snarky)
Also, the SO/SE people have long maintained that Google is their homepage, and from this view it's easy to see why they would encourage people to answer their own questions: so that SO gets the googlejuice instead of some blog.
On the other hand, to the degree that we believe that individual blogs are good, we absolutely should worry about auto-answering.
That's an interesting concept that I'd never even considered. I then realized that I couldn't even remember what the stackoverflow homepage looked like, yet I utilize that website daily.
It doesn't seem to be harming the stackoverflow and associated sites, so I guess it's not a bad thing.