Actually I was just experimenting on how forum posts affect SERP, particularly on titles of forum posts. Some forum post I made use to have the key phrase "targeted link backs" in the title - during the time we held the top position for that key phrase. I decided to change future title posts with "targeted backlinks" (which we never ranked for before) on the title to see if it will affect SERP. After a month, I saw that we were ranking #1 (sometimes #2) for the latter key phrase and lost ranking for the former.
So definitely, these are factors that affect SERP. 
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