There's a difference between sharing ideas and copying other's work.
Since this community is made up of individuals, there's not going to be a lot of serious fighting over intellectual property. But when you rip off a large corporation... Their lawyers are going to care.
In the case of the cat skeleton on the side of the dude's car... It's obviously infringing upon the intellectual property that is the livery for a race car. Is the driver (Bucky Lasek) going to care? Definitely not. Will the owners (SRT) of the vehicle care? Probably not. Will the owners of the image (PUMA) care? They might get their panties in a twist.
Stuff like monetary gain and free advertising doesn't mean anything either. If you duplicate someone else's work without their consent, it's illegal. The crazy part... It's really not that hard to get consent. You just gotta ask.
I work for a company that specializes in copyright enforcement. The bigger companies care more about it than you think.