In a new article on compulsive shopping, there is discussion about including this behavior as a "mental disorder" in the new Diagnostic and Statistical Manual of Mental Disorders (DSM).
Considered the diagnostic bible of mental health professionals, the new edition is due out in 2010, and there is discussion about including the so-called "behaviorial disorders." This group of disorders includes internet addiction, compulsive gambling, hypersexuality and compulsive shopping.
As a psychotherapist, I have treated compulsive shoppers for many years. All describe the cycle of exitement (buying), remorse (second thoughts), and guilt (low self-esteem) that is common with compulsions. Like a dopamine squirt to the brain, the shopper seeks out the next high with purchases that they don't need, purchased with money they don't have.