Self-Publishing vs. Traditional Publishing

I'm a little more relaxed about the issue of self-publishing vs. traditional publishing than I was a few days ago, though I still have a number of questions floating around in my mind. My S.O.'s self-published book hit a record high again on Amazon.com's sales rankings with a rank of 39,000. My only frustration with these rankings is that we never know why the book rises and falls. Was it a result of certain marketing efforts on our part? If so, which ones? Is it word-of-mouth? If so, how do we take advantage of that?

In the meantime, I found some helpful articles on Helium.com about self-publishing vs. traditional publishing. Below is the link, for those interested:

http://www.helium.com/items/1338021-self-publishingself-publishing