Amazon does allow books on multiple devices at same time (actually its on a book by book basis, with some newer books restricting the amount of copies) but the vast majority of current books are allowed on more than one device at a time, its one of the major advantages of kindle, you can be reading a book on your kindle, pick up your ipad and continue from the same place, then perhaps move to your Pc and do the same thing again, all thanks to whispersync. Me and the wife share a kindle, ipad, two iphones and I have my work Pc setup for kindle as well. I have all the books I'm currently reading available to me on all devices at the same time. Just make sure if your sharing with other people your not reading the same book or your bookmarks will get all mixed up.