For instance, here's one of the aircraft carriers from Pearl Harbor making a cameo in the first Transformers film.
Touchstone Pictures, Paramount Pictures
That aircraft carrier should be retirement age with a snowy-white beard by now.
Perhaps that was just a little self-homage, but this isn't a one-time thing. Remember Bay's The Island, that two-hour Xbox ad starring Ewan McGregor and Scarlett Johansson? Of course you don't, because nobody saw it. This makes it the perfect film from which to "borrow" shots that Michael Bay doesn't feel like taking the time to redo. As pointed out in this YouTube video by filmmaker Jermain Odreman, Bay Frankensteined footage from a car chase he had filmed for The Island and shoved it into Transformers: Dark Of The Moon. Seriously -- barring a few CGI touch-ups, it's the exact same footage:
DreamWorks Pictures, Paramount Pictures
Bay was angry when those rollerblading robots wandered into the shot
for The Island, but they sure came in handy later on.