Just announced by Google's Senior Vice President of Engineering +Vic Gondotra, Google+ has finally arrived for the iPhone! Many people have been waiting for this for a while, and it seemed like it would be held up forever in Apple purgatory, but now it's available for the iPhone 3G, iPhone 3GS, and the iPhone 4. Support for iPad and other Apple iPhone devices is in the work, so be patient. You can download it directly from the iTunes store.
There have been reports of issues with the app, such as freezing and crashing. Some of these issues are already in the process of being fixed. If you have issues, send feedback to Google+!
Did you download the iPhone app yet? How do you like it?
Edited to add update: Make sure you are downloading the latest version of the iPhone app. If you downloaded the version right when it was released, it may have been an older test version. Get the newest version!