I researched this recently and came to the conclusion that you can't really make any money with POD, particularly if not selling direct, but still POD might be useful to determine market potential.
Here's the list of links I compiled - all are POD except MR's article and 100 Books.
http://www.lashier.com/home.cfm?dir_cat=69813
Some of the PODs do have quantity discounts, but usually fairly small. If you're willing to bet that you can sell 1000 copies, the 100 Books method brings the cost to 1/3 or less of POD.
- DL