Alan Tudyk's rather terrifying transformation from a meek assistant to an unhinged badass is reminscent of his role on Dollhouse. His out-of-nowhere hacking skills also add to the Split Personality feel.
Defictionalization: The Wreckers made an appearance in car form during the parade laps of the 2011 Daytona 500
Deleted Scene: The Twins from Revenge Of The Fallen were intended to be in this movie but were removed in the final cut. If you look carefully you might be able to see their vehicle modes in a distant line-up shot.
Doing It for the Art: Bay managed to get the entire city of Chicago to help them with filming the entire climax. Shia LaBeouf and the other cast members were in awe of how much access they had to the whole of the city on a daily basis. Plus the entire wingsuit sequence was put in after Bay saw a TV special on them, and they are actually flying between the skyscrapers wearing portable 3-D camera helmets.
No Export for You: Hasbro cancelled the American release of the sixth wave of DOTM toys, including the much-anticipated Human Alliance Soundwave, due to low retailer demand. The cancelling of the line also means a Dino/Mirage toy is probably never coming.
The Other Darrin: Sideswipe has a different voice actor than he did in the second film.
Product Placement: The Wreckers take the appearance of weaponized NASCAR Sprint Cup Series as their car modes (armorized versions of the #42, #48 and #88 cars of Juan Pablo Montoya, Jimmie Johnson and Dale Earnhardt, Jr.). The Wreckers themselves also circled the track during the pace laps of the 2011 Daytona 500, at which Michael Bay and Josh Duhamel were the grand marshals who gave the starting command.
The Twins from ROTF were scripted into the movie but were carefully removed from the final cut (you can briefly see their vehicle modes in a line-up shot). Their roles would have been to be killed by Sentinel Prime after he reveals himself as a traitor by killing Ironhide. Maybe they weren't confident in getting an Alas, Poor Scrappy reaction....
They advertised Shockwave as the Big Bad/an important enemy as part of a "misinformation campaign", where they would deliberately lie about certain aspects to keep information and spoilers about the film to a minimum to prevent plot twists having no impact, such as Sentinel Prime being the real Big Bad and Soundwave's car alt-mode.
Bumblebee's new look is to represent his maturity from a simple guardian to a full-fledged warrior. His stripes are also moved farther out from the center of his vehicle mode.
The Twins from Revenge Of The Fallen were killed by Sentinel Prime moments after he destroyed Ironhide but this wasn't included in the theatrical cut for pacing reasons.