Yes, there are some ads at the bottom of some posts on my blog. I have no control over them. This blog is free from WordPress and hosted on their servers. The advertisements are what keeps WordPress free.
From their blog post about the Ads:
At WordPress.com, we sometimes display advertisements on your blog to help pay the bills. This keeps free features free!
We only run them in limited places, and we do not show ads to logged-in readers, which means only a very small percentage of your page views will actually contain ads.
Link in article: