Its probably legit, or close to it. The rebates on the 2010 are pretty big right now, and that advertised price probably takes them all into account. They already have discounted heavily off of the MSRP and then applied all rebates to achieve the advertised price. My dealer has a 2010 GT FULLYYYY loaded advertised right now at $21,xxx most dealers are doing anything they can to move them. The only real thing you should look out for is whether or not any of those rebates are ones you don't qualify for (ie: conquest cash for people coming out of competitive make vehicles)
Here is one thing to also remember: If you are going to finance the car for more than 3 years, GET THE EXTENDED WARRANTY (unless of course you plan to modify then any warranty is useless) I work as a Service Advisor and the Ford PremiumCare Plan which you can get for an extra few hundred bucks is worth every penny. I always have customers who are out of warranty giving me a hard time about repair costs, yet also refuse to get an extended warranty. Also...DO NOT opt for the third party warranty plan. ONLY choose the Ford plan or you will regret your decision. Just my .02
EDIT: Didn't read your last post...you will be very unhappy with the quote you are given for a lease on a 2010. The lease programs are TERRIBLE on the 2010, not all rebates apply to a lease and the ones that do apply are very specific (college grad, military, conqest, etc), because of that the sale price used to calculate the lease will not be the one you see advertised, and you will end up with a high payment.