You can't share / copy / email an ibook from the iBooks app. If the other person uses the same iTunes account as your self then they can redownload the ibook (if it's still in the store) via the Purchased tab in the iBookstore in the iBooks app - if you don't use the same account then you could potentially log into your account on their iPad and redownload it, but you might tie their iPad to your account for 90 days : iTunes Store: Associating a device or computer to your Apple ID
Purchased content is not meant to be shared from one Apple ID/iTunes account to another one. You have never been able to share purchases. This will be changing to some degree in iOS 8, but for now, you can't share content without jumping through hoops and running the risk of locking yourself out of your own ID for 90 days as was pointed out by King Penguin.