In the alleyway when the Power Corps first reveal themselves, as people are rappelling from the rooftops, you see members with camouflaged jackets turning away from the wall. When Marion is introduced, they turn away from the wall a second time.
When Shuko and the gang are in his office listening to the computer read the information on the Lee brothers, it says Billy is 17 and Jimmy is 18. Right before the Lee brothers fight the gangs in the junk yard there is a closeup of one of the gang members of the Clowns reading the Lee's information. It is says Jimmy was born on 2/24/90 and Billy was born on 2/17/92. If the movie takes place in 2007 that would make Jimmy 17 and Billy 15.
The movie takes place in "New Angeles", California, however when Chief Delario goes outside of the precinct after telling the officers that they are going to take back the streets, an Ohio flag is shown flying on the flagpole.
The goof item below may give away important plot points.
Jimmy allows Abobo to drive the "Dragon Wagon," thinking he is really Billy who has possessed Abobo, but Jimmy is the one who has the medallion half with the power of the soul; Billy has the half with power of the body, so he shouldn't be able to possess anyone.