No, they don't save you any money unless you count the gas it takes to get to the bookstore, or shipping, or other related expenses.
But I love my Kindle. I really fell in love with it on vacation since I could load up several books and carry them all in one slim package. I also like the feature where you can "sample" the book by reading the first few chapters before you decide to buy.
I also really like it for Mo. You can increase the font size so that the page isn't overwhelming and he isn't so intimidated by by long books because of how much of the book is left to read.