I was reading a few articles on line (a few years old but still good reads) about Wikipedia's role in SEO and I am trying to make sense of what exactly the benefit is and how one would use it for a particular site. For example, is I doing SEO activities for a site that sells custom made guitars, how would I use Wikipedia to enhance my SEO initiatives. I am also curious to know how widespread the use of Wikipedia is in SEO functions.

Good question. I also wondered that myself. I knew a few clients who submitted a few articles about their client's businesses or products and those pages were never posted. It does help if the original poster on Wikipedia have already submitted a few articles in the past that were non-commercial.