That being said, I'll share two stories incase they help anyone...
[1] I have 5 friends (from different social circles and age groups) that have used Carmax to both buy and sell their cars (new and used) -- they have ALL come back with praise for the company on the process, even after comparing car prices online diligently before heading in. Similar the Saturn promise of "no haggling" this shopping experience seems to be fairly solid. I have not done it yet, only what I have heard.
[2] My best experience buying 2 new cars as well as a friend buying 2 new Subaru's that I shared my strategy with went as follows:
Read owner's forums for the car(s) you are considering; Edmunds and standalone owner forums were great for this.
Get a sense for the average price people are paying for the cars around the country. If you see a range of $33,000 to $36,000 then use an average of $35,000 (for example)
Call a local dealership, tell them the car and trimline you want and exactly how much you will spend OUT THE DOOR (always out-the-door) and to call you back if they can do it.
Sit at home and wait for a phone call.
Go in, look at the car, sign the papers and drive home.
I had two trade-ins when I did my cars so my out-the-door price was lower by how much I estimated a fair trade-in value for my used car was (using kbb.com and edmunds.com and some common sense)
Overall the ease of the process was great with no BS and no haggling.
If you like haggling or your goal in buying a new car is to mentally crush the sales agent, then you won't need this strategy... but if you hate wasting your time and want to get a fair price, it works wonderfully.