Gregory, my only data point for a 'merchant' accepting txns which have zero conf WITH widespread network propagation (say, >70%) is blockchain.info's now-defunct laundry service. 0conf w/o net. prop. was never accepted, 0conf w/ net. prop. was accepted for 'small' amounts, 1 conf for med amounts, 2 conf for large amounts, and 3 conf for extra large amounts. Anyway, you knew all this better than I did, but you asked so here you go. Thank you for explaining the greedy-miner strategy for safe confirmations. The problem I see with that, is the merchant needs a fast connection to "destroy" the transaction in time.
http://blockchain.info/charts/avg-confirmation-time
12 minutes to one confirmation isn't terrible for the purchase of digital goods...but in person transactions would be limited.