This has been going on in our class for the past few weeks, with a lot of success. At the start of the term I put a folder at the front of the classroom. On the front of the folder, in very big letters, were the words 'Mystery Book'. Inside the folder was, unsurprisingly, a mystery book (I chose One Dog And His Boy by Eva Ibbotson). I left it there for a couple of days to build interest, making reference to it every so often ('Ooh, that looks exciting! I wonder what's inside!' type comments).
I then asked the children who would like to read the 'Mystery Book'. Every single hand in the classroom went up immediately. I then explained that if a child wanted to take the book home and read it, there were three requirements. Firstly, they would have to write a ten word review of the book in a jotter which was also inside the folder. Secondly, when they had finished the book, they would get to choose who to pass it on to next. Finally, and most importantly, they weren't allowed to tell anyone else what the book was.
Four weeks down the line, about a third of the class have already read the book and, as far as I know, the secret is not yet out. They love the whole 'hush-hush' aspect of the idea and there is always a lot of excitement when the book reappears in school.