The feature was already on the Android app, and it finally reaches the iOS app, although I find this feature a little annoying as everyone on your G+ account can view it. However, it is a neat backup option for all your photos.
- The What’s Hot stream
- Shake your phone to send feedback: Google+ Update: Shake and Send (Sexy) Feedback from your iPhone
- Various bug fixes and performance improvements
Google also says that the Instant Upload feature is only active while the Google+ iOS app is open; it shuts off when you close it. Re-opening the Google+ app resumes your photo & video uploads where they left off.
You can download the update over here.