goodreads, a social-networking site for book lovers has updated their iPhone/iPod app, to include a barcode reader for easy cataloguing of books, whether ones you want to read, or books on your bookshelf. I had created a workaround for this with RedLaser on the iPhone, but this is much smoother and allows for multiple books to be entered before “processing” them in your account.
My eldest daughter reads prolifically, so to keep track of all the books and allow her to rate and review them, we’ve taken to recording them on goodreads. Also, all of your data is exportable to a spreadsheet if you ever get sick of the site but want to keep all the book info.
Friend me on goodreads here.