Let's say we aren't particularly concerned about the quality of the ice because we are using it to chill beer or keep beer cold or something like that. (I need to bring a case or so to a BBQ tomorrow.) Let's also stipulate that you have the use of a built in ice maker (so that you are not constantly opening and closing the door) in a relatively new (2-3 year old) efficient refrigerator.
What is more cost effective given the Boston area's outrageous water rates and the cost of electricity - making your own ice or buying ice. Figure 5 pounds for $1.25 at the store?
Nerd among yourselves ;)
P.S. I kind of guess the answer has got to be making it yourself, otherwise places like Brookline Ice could not make any profit. I mean there can't be that big economy of scale.