Grapes can be toxic to dogs. Here's an article that's been verified by snopes on feeding dogs grapes and raisins. They can develop acute kidney failure from eating grapes or raisins. Very scary for dogs! http://www.snopes.com/critters/crusader/raisins.asp
Sorry Titaniumcranium! I didn't mean to thread jack. This important question was asked, so I answered it.
My non-gardening neighbor has a massive grape vine covered in grapes. I'm waiting for them to ripen so I can swipe the ones that hang over the fence and start my own grape wars!