Google announced the upgrades in a blog post, saying they'd be available today on the web and in a new app download in Google Play.
Although the blog post says there are 18 upgrades, Google senior vice president Vic Gundotra posted on Google+ to say there were actually 25, including bigger post photos in the iOS app. The app also has a new icon, reducing the size of the "G" and "+" characters.
Google+ instant upload has always backed up all photos and videos, but the maximum picture resolution was about 4 megapixels. As of today, those photos can be any resolution, but free storage of high-res photos is limited to 5GB (users can purchase more).
With Android 4.2, the second iteration of "Jelly Bean," Google introduced photo spheres, or 360-degree panoramas. Now users can share those pics in the Google+ stream on mobile, and anyone using a device with Android 2.2 "Froyo" or later can view them.
Google+ Events is getting upgrades, too, finally adding some of the features that have long existed in its major competitors, Facebook Events and Evite. Now event hosts can send messages to specific guests and see who has viewed the invitation. Also, you can invite people by simply sending them the URL of the event, and guests can now say how many people they're going to bring. Finally, hosts can create an event by starting with a duplicate of a previous event.
Hangouts, the live, multi-person video chats that have been a big differentiator for Google+, have been improved as well. For starters, users can now connect via hangout with people with very little bandwidth as low as 150kbps. Hangouts On Air, which lets users "broadcast" hangouts to many viewers, gets a cosmetic tweak: If the host is the only participant, the "filmstrip" of faces below the screen will go away.
Extra bonuses for Android users: animated GIFs will now show up (they already work on the web), Google Now is getting birthday alerts, and there's now a Google+ widget for your phone or tablet's lock screen.