I would get an alignment and ask for the readout when done. May as well get a re-balancing of the wheels as well.

 

Tire rubber is actually a liquid, much like window glass is, and if they sit too long the rubber actually does drop (move) enough to cause this "flat spot" effect. This can be temporary and the tire should round out with driving and after it warms up, or permanent, at which point the internal belting and casing of the tire has also shifted-- this results in permanent tire damage

Not to get too technical (it most likely is not a flat spot) but this is all based on harmonics and if the vibration on your steering wheel occurred at every rotation (low harmonic flat spot) and not at specific speeds (say 70-75mph), it would be a temporary flat spot. If you felt it only at certain speeds (e.g., 60-65mph), it would be called a high harmonic flat spot-- these are permanently damaged tires. What a dealership may try to do if it is a high harmonic flat spot, is overcompensate with the weights-- just be aware of this. In this case, your tire will wear out prematurely and since tires aren't warrantied, you eventually will have to buy a new one and will have no recourse.

However, I would imagine the car would have to sit for months for this to occur, and it's a 2008.

Nonetheless, the rhythmic vibration at certain speeds is most likely a balancing issue, as other have pointed out.

 

So I have driven from NY to Atlantic City, and NO vibration still. I find it very odd that it hasn't happened once after I brought it in. Maybe they balanced the air pressure in the tires...I still do feel slight road surface vibration, but I have always felt that, as I think it is normal for a sports sedan