I think it really sends the message of our love of books and that we didn't just love books when we were a kid in school. It is also a great way to learn about the interests of others in our building and our district. I like seeing the titles of the books that others are reading.
Finally, I find that it makes me find the time to read more. I don't want to email someone for 3 weeks and have the same book listed all of the time. It makes me accountable to finish the book and move on! :)