There is a lot of discussion in The Book World about the advantages and disadvantages of having agents & publishers versus self-publishing. For myself, I believe that having a good agent and a publisher I can work with is worth its weight in gold.
Author "Jay Lake" has an excellent column on his blog that is more than worth the time to go and read, regardless of whether you're a teacher, student, aspiring author or one who is already already published.
The article is entitled: What my publisher does for me, and why I won't just quit.
NODS & ENDS
One of my favourite commercials: How the snow-plow driver gets to work