Eoin--
Well rude or not, it comes down to legality... and the law would ask "would a reasonable (read: average) person allow trash to be strewn all over their yard?" The answer would be no. A reasonable person takes trash from his or her house and places it in a trashcan for pickup by the city/county. A reasonable person does not take trash from his or her house and litter the yard with it.
About having a car on blocks--that most likely wouldn't be against the law. It's different if, as Mr craphead [uh, interesting nick you've got there] said, you choose to live in a community that enforces rules on how your property looks. In that case it is your choice to live in said community, and if you choose to live there you must abide by their rules and keep your property up accordingly.
l2c
Edit: Seeing as you don't live in an area with a homeowners association, you're not required to keep up your property, but it's a good thing to be neighborly and show a little respect for other people every now and then.