No, the Google+ iPad app hasn't been released, but Google has laid out the specifics of how developers can update their applications to incorporate the Google+ platform's features. Before getting into all of those API details, Google warns developers not to get too ambitious about releasing their apps with this code — this is a developer preview, after all.
The first feature that Google is offering iOS developers is a Google+ sign-in button. This works just like the browser-based button, letting users log-in with their Google credentials instead of creating another account. Google has also provided code for Share and +1 buttons, each working just like their respective buttons on the web. One of the most compelling features for developers, though, may be the option to integrate with Google+ History. This works a bit like Facebook's so-called "frictionless sharing," for example, where a users' in-app activity will automatically populate in their Google+ timeline, adding visibility to a developer's app. The Google+ platform also supports a broad API that will allow developers to bring in user profiles, posts, and comments, but whether there will be enough latitude for creating alternative clients has yet to be determined.