If you read many books it gets tricky to remember which books you've read, what it was about and what you thought about it. I had this problem but I figured there had to be a good way to keep track of your reading. I found the website Goodreads.
At Goodreads you create a virtual bookshelf where you add the books you've read. If you want, you can rate the books and after you've rated 20 you'll get suggestions about books that you might like based on what you've read and liked.
That's not all, you can search for books by entering a genre or a subject that you want to learn more about. Then you can read reviews written by other users that might tell if the book is fitting your expectations and needs.