This is great news for user of blogspot.com or blogger.com. It is even easier and more flexible with this new function. There is some limitation that you could only have Google Adsense for the inline advertisements and some of the old customized templates will not work with this, you may have to consider newer templates.
But you did not pay for hosting or the domain, therefore everything you earn from Adsense or any advertisements program is pure profit (deducting your own time & pay).
To learn how you could show adsense between post.
Do you know that when your blog become famous, whatever you blog about will make you more famous and more money?
This is what I call blogging momentum. When your blog gain momentum to excel, most people would actually be supporting you, but when your blog is not in anyone radar, you will get noting.
If you look out there, there is some blog which I used to visit and carry pretty good content in the past, but currently does not update often, and the content is no longer good. But the blog is still famous and a have a lot of visitor. This is because the blog have already got its momentum. It takes hardwork to get a blog to have everyone trust and loyal reader, but once you have reach such a point, it is going to be much easier. Anything you have started, or any community you are in, it would eventually be success as long as people knows about it from your main blog.