Beginning in April, Google (which owns blogspot.com) will begin tracking user activity via a cookie. This cookie will then determine what ads might be most appropriate for you, based on your interests. People who frequently visit ESPN.com and CNNSI.com, for example, will see sports-related ads. The logic is that you will be more interested in these ads than you might be in ads that are simply related to the content of the blog.
For more information, or to opt out, go to Google Privacy Center. There is a blue "opt out" button in the upper right corner. If you do not wish to have your activity tracked, please take a minute and opt out.
If you opt out, you will continue to see ads, but they will be related to the content of the blog - something that does not require a cookie.