Yes. There will be ads. For what Yahoo paid for it, Yahoo would be foolish not to monetize Tumblr to recoup their investment. It is also a trap that can lead to Tumblr becoming a ghost town. Hopefully, Marissa Mayer means it when she states that ads will be tasteful. Sprinkle too many and the counter culture and millenials will eventually find new pastures. Restrict content and they will feel repressed. Proceed with caution because the task at hand will not be easy.

http://www.pcmag.com/article2/0,2817,2419196,00.asp