This report is a worthy (if lengthy) read about body armor.
The IACP/Dupont (Kevlar, natch) publishes a list of people who survived attacks because of their vests. I say 'attacks' because there are documented cases of officers lives being saved while in an auto accident, or a non-ballistics attack (read: baseball bats, blunt objects). They also estimate the average cost of an officer's life loss at 1.3 million dollars. Surely the cost of a vest is justifiable by that figure.
Plus, to the spouses, children, and families of the officers, $1.3 million is a paltry sum. We'd much rather you come home. Wear it, and be safe.
IACP/Dupont Kevlar Survivors' Club. 3000 as of June 2006. WEAR IT. We love you.