Saw this little nugget on Jayki's site. Very interesting:

NASCAR featured in Transformers 3 movie: NASCAR style racecars adorned in the colors of Juan Pablo Montoya, Jimmie Johnson and Dale Earnhardt Jr. were competing in downtown Chicago in a little race of their own; complete with armor and machine guns. Filming for the third installment of the wildly popular Transformer movies was taking place over the course of the last week and although the exact plot hasn't revealed, it would appear that NASCAR will be playing a role. Fans who were at the location sent snapshots of cars painted to resemble the Chevy's of the #42, #48 and #88. The cars were morphed and included loads of heavy weapons. Last year the cars of #24-Jeff Gordon and #39-Ryan Newman bore special paint schemes of the movie during the fall race at Charlotte, but there has been no word on the exact involvement of NASCAR.
The areas in Chicago that saw filming included LaSalle Street, Michigan Avenue, Bacino's of Lincoln Park at 2204 North Lincoln Avenue and around the "Sears Tower". According to fans on location the Michigan Ave scene where the NASCAR style cars were spotted was filled with crashing and explosions.
The final film in the live action Transformers series it is directed by Michael Bay and produced by Steven Spielberg. It is the sequel to Transformers and Transformers: Revenge of the Fallen and is scheduled for release on July 1, 2011 in Real D 3D theaters nationwide and in IMAX 3D.(NASCAR Examiner) and see some images at www.tfw2005.com.(7-12-2010)