I was driving myself crazy trying to figure out where this newest option was so that I could add "reactions" to my blog posts! I thought that the most likely place to find this newest option for Blogger.com blogs would be in the layout section under "add a gadget" - but it turns out that this isn't where it is - sort of..........
Once you go to the Layout portion of your blog, then you have to click on the link to open up your blog post option and that is where you will see the "reactions" options that you can add to your blog.
By the way, I can't add the "reactions" option to this blog because this blog uses the template and not the layout version of a blog template.
But I will add it to my Adsense Consultant Blog.
If you are having problems with this latest Blogger.com Add-On, you can post about it here on the Blogger.com Help Message Boards! This particular link will take you to a "sticky" thread where you can post if you are having problems using the new "Reactions" add-on for your blog!