One of the cool applications I found on Facebook are those that let you show what books you read or are reading at this moment. The problem is there are multiple applications doing the same thing and I bet you cannot exchange data among them. Just looking at the profiles of my friends I saw three of them: Visual Bookshelf (the one I also use, being the first one I stumbled upon), Shelfari Books, iRead. I wish there was a monopoly in this domain :)
By the way, I finished the third book from the Harry Potter series. I started reading the forth one (the goblet of fire).