Carl Trueman's blog post and short review of Matthew Levering's The Theology of Augustine is well worth a read. Here's a snippet:
The pears incident in Book Two is, of course, the moment of Augustinian fall. For all of the emphasis on sex and sin in his work, it is the incident of petty theft which serves to show the depravity of human nature and the fall from grace.
Like that of Adam, the crime involves a garden, a tree and forbidden fruit; it involves peer pressure; it is so trivial that every reader can identify with it; it involves no motivation other than the desire to transgress a rule, to assert autonomy (divinity) in the face of established authority; and, given Augustine's coming to Christ under a tree in another garden, offers a literary device of power and beauty within the narrative which seduces the reader in manifold subtle ways.
Who can read the tale and not be drawn into the story - and into the trap - which it sets? It is a far more eloquent analysis of sin than that found in any dogmatic textbook.