They claim that the wheels are cartoonishly large out back and lines, and the fact that GM is a major player in the film, would seem to suggest it's some sort of GM concept car that was never seen anywhere before although not the Corvette ZR-1, as some have claimed.
It's also got the same concept mirrors that GM loves to use and kind of looks like Bumblebee's evil Decepticon twin. The car has scissor doors like a Lamborghini. Some say it was a concept sort a cross between Cadillac Cien or Corvette C7.
Not sure if this one was to be confused with the most recent Saab Aero, but the silvery paintjob does cause confusion. I bet Bay would not want too many cars sharing the same color even though the make was different. What say you? Any guesses??
The mystery car

Cadillac Cien

Corvette C7

Autoblog claimed that a silver mystery car was spotted during the recent shoot in Pennsylvania. Car fans are all making guesses of what sort of car was that used in the set.