The first or second tag, sorted by popularity, that is not in the title is prepended to the title. 

In your examples:

 - http://communitybuilding.stackexchange.com/questions/1113/how-do-we-maintain-answer-quality-when-everybody-thinks-theyre-experts The top tag of the two on the question is [tag:content-curation] with 19 questions (versus [tag:community-standard] with 7), so it is added to the title

 - http://communitybuilding.stackexchange.com/questions/667/advantages-to-storing-content-locally-vs-outsourcing-it-to-a-3rd-party [tag:small-communities] barely wins on this question with 20 questions, so it is added to the title.