According to the pull-down menu here, it is now live for the New York Public Library (but not Brooklyn):
http://ebook.3m.com/library/en/patrons/
Book selection is currently tiny -- nothing like the promised full Penguin backlist.
My family has a New York Public Library card, and just borrowed our first 3M book (
The Canal Builders: Making America's Empire at the Panama Canal by Julie Greene).