So, apparently Windows 8 has advertisements within some of its core apps, a rather unprecedented move and one I am surprised there hasn't already been a commotion about. Even if you don't care about ads per se, there is a bigger implication than having screen space within parts of Windows 8 dedicated to generating revenue for Microsoft:
We can't talk about the inclusion of ads and not mention the “T” word: tracking. I haven't been able to find any information on whether or not Microsoft's tracking the ads you are clicking on, but if that is indeed the case, we'll find out soon enough. Unlike Windows 7 and earlier, your entire Windows 8 account can be tied to an e-mail account, so it would be rather easy for Microsoft to track things on a personal level - much like how Google does with its search engine, e-mail and so forth. This alone gives good reason to be concerned.
Can you imagine the outcry if the iPhone came out of the box with ads in its Weather or Stocks apps?