If someone joined your forum and began to post topics citing their own website or blog as a source, would you consider this spam, or not? This is assuming that the topics are completely legit, and don't break any other rules.
It would depend on the quality of their site and whether or not it was actually a legitimate source of information. If their blog articles were just scraped from somewhere else, then I would definitely consider it spam and ask them to either remove the incorrect citation, put the correct one, or remove their post altogether.
I don't see a problem with it. If the content is of decent quality, and the give credit where credit is due and they aren't making it sound like just a spam post advertisement, then I don't see anything wrong with using your own website as a source of information.
I think it's spam. It helps the member by creating backlinks, while it hurts your SEO score because of duplicate content. It's spam, especially if it's done repeatedly.
It would really depend, if they did it now and again and it was in direct relation to a discussion and helped to further the discussion I would be fine with it. If they were purposely creating threads just to be able to link to their site I would not be so nice about it
I suppose it would be fine, but if they aren't posting any content from any other sources, ever, its easy to see they're only in it for the promotion. After a while the topics would start to feel like spam even if they weren't.