[link|http://www.edmunds.com/advice/incentives/holdback/|Edmunds on Dealer Holdback].
The trouble with buying a car these days is that even if you know the holdback and the incentives and ..., you still don't really know what the dealer is paying for the car, nor what their bottom-line price is. How much of their "advertising fee" is legitimate? How much of the "paperwork fee"? And there's always the issue of how they screw around with trade-ins (if you have one).
It's good to be informed as much as possible, but there are still hidden transactions between the manufacturer and the dealer that affects the price.
Edmunds has a lot of information on stuff like this, but much of it has been hidden so that it looks like you have to request a quote from a dealer to get it. Use Google to drill down.
Cheers,
Scott.