For sharing on the kindle, we discovered if you deregister your kindle and, for instance, re-register it in my name, my books are in the archive and you can transfer them to your kindle and then re-register it back in your name and the books will still be on your kindle. Not sure if this is legal or not... but we've done it amongst ourselves.
If you are transfering books from one Kindle to another you can do it via computer or wireless. Just turn the Kindle on to your network and go to sync and all books are transfered in about a minutue. Too easy, even I could do it!Gert