What is a spider with yellow stripes on it's back in Michigan?

I assume your talking about the common garden spider: the spider in question is most likely the black and yellow Argiope (Argiope aurantia), one of the species of orb weavers. They are found throughout the North America (where ever there is a warm but not overly hot summer).

It is not likely to bite you but if you forced it to bite you by pressing it against your skin for some amount of time, the bite would result in swelling and discomfort. It would be a severe and unusual allergy that would result in anything more life threatening from a garden spider bite. they should be seen as a welcome site in any garden if you choose not to use insectisides as these will cut down on grasshopper populations in a very big way.