Google's Google Play Books market isn't just for Android devices. There's also an iOS app available to read content purchased on that market, and it's just been updated with some new features. Bookmarks let you place a bookmark by touching the top right corner. You can also highlight and even put notes on specific text as you read. You can search for and define certain bits of text, and use the +1 button to share whatever you're reading on Google Plus.
Are we too kind to pass on mentioning that iBooks already had all of these features, save for the Google Plus integration? Apparently not. But if you've got content on Google Play already, at least you'll have an easier time of reading it now, even on an iOS device.