The official Google+ iPhone app is now available for download at the App Store.
The app gives you access to Stream, Huddle, Photos, your Profile and Circles, and has a Notifications bar on the bottom similar to the Facebook iPhone App.
The App at this point is buggy and slow, and has crashed constantly for me when trying to upload a photo. Other reports online point to the app crashing on iOS 5 beta 3, along with iOS 4, and will not run on Wifi only iPads.
UPDATE: Seems that Google has already updated the app, now listed as Version 1.0.1.1809. The update is to fix “various bug fixes and performance improvements” and better support for Huddle and attaching photos.