This is the story of a pastor's wife who realizes her middle class lifestyle puts her among the richest people in the world globally (she lists the percentage in the book, it's something like the top 10% of people on the planet). From there, she decides to make a temporary change in her lifestyle each month to help her understand how good she really has it.
Stylistically, this is a very informal, chatty sort of book. The vast majority of the book's content is also on her blog. I found the book to be a bit naive in a sweet way. It's almost as if she doesn't realize there are poor people in America as well, who don't go out to fancy restaurants or have hundreds of pieces of clothing.
If you're a middle class christian and like Shane Claiborne's writings or the other emergent church/christian simplicity books, you'll like this. If you're already living at the poverty line and have simplified your life, you may find it a bit off-putting. And if you're not sure if you want to read it, start with her blog.