Linda - I was wondering the same thing. I have yet to see any of these types of domains rank for any competitive local terms but I think it's because they are just too new. We'll probably start seeing them in years from now. They've only been around a short period of time and I think Cody is correct that age is a really big factor.
At least in the automotive vertical, there's some people pushing them claiming that the exact match will rank over the .com and a whole range of fluff that makes my head hurt.
Yes, an exact match for a keyword no one is searching on will cause a .cars domain to rank for that term.