small correction sir, it's their credit (debt) rating that was cut to high-yield, or 'junk' status - not their stock. in other words, S&P is saying that GM and Ford are now riskier to lend money to, so you should charge them more interest. ;)
their stock isn't doing all that well either because of this and other reasons, but depending on what you believe, they could be a good buy-low target right now.
one other problem they have is with the worker's union; i.e. they're getting saddled with "legacy" costs -- pension, benefits ng retired workers -- as well as very restrictive CBA terms(bawal daw magsara ng plant ung GM, and all plants should operate at at least 80% capacity).
hopefully with a little belt-tightening, makakaraos sila sa short term. but they have to solve their most fundamental problem -- i.e. no one's buying their cars.