Microsoft is not accepting Bitcoin for Microsoft products. Microsoft is only accepting Bitcoin for Microsoft partners who sell through Microsoft's online store system. From the Microsoft page: "You can only use Bitcoin to add money to your Microsoft account and then purchase digital goods at select Microsoft online stores. You can’t use Bitcoin to purchase Microsoft products and services directly at this time."
But they don't rule out the possibility, hence the "You can’t use Bitcoin to purchase Microsoft products and services directly at this time."
Either way it doesn't matter, the fact Microsoft is associating itself with Bitcoin at all adds credibility, and - over time - is going to pique interest from a broader audience. I don't know if we'll see a huge rally now. That depends if speculators want to pump it. But long-term this is very healthy for Bitcoin.
