X-Plan vs. Haggling

Depends on the dealer and if you are trading anything in. I was told x plan gets you the price the dealer pays. That does not include volume discounts, holdbacks and a bunch of other stuff. Ford also pays each dealer $200 or $300 or so for each vehicle it sells on an x plan. My dealer will honor an x plan but what he allows you on a trade decreases by about $1,000 or so. That way he can make up what he didn't make on the new car by selling your trade-in.
Compare dollars to dollars. I figure an x plan with a trade would save me $300 to $400. Without a trade an x plan would save me about $1,500 on a new Fusion for my daughter.
The savings also varies from vehicle to vehicle. And on some vehicles the dealer may not accept x plan. Many didn't accept it at first on the 2005 Mustang. Mine did and I saved about $1,000 off sticker.

Makes me glad I got to use the A plan

(My grandfather worked for Ford, and I also got to use the retirement rebate on top of that)

I have heard several varients on X plan pricing also. You might find your answer here:
http://www.umd.umich.edu/univ/staffsen/forddiscounts.htm

I used x plan and i got the car for $35 under invoice and 500 cash back on a 07 GT. In total i saved a little more then $2400

I did an internet sales deal on my '06 GT Premium and not only did I get the 0% APR/72 months, but it was also $500 under invoice at $27,750. The only thing that kept it from being fully loaded were the 18" wheels.