On the face of it, Shared Photo Streams are a cool idea: Say, you're on a trip and want people to see your photos as you take them. Sure, you could upload them to Twitter or Facebook, but wouldn't it be a lot easier if your friends got those pictures delivered right to their devices?

When you create a Photo Stream, your contacts will get an email and a push notification inviting them to join the Photo Stream; you'll get another notification when they join it. Once they've done so, they'll get a push notification each time you add an image (or images) to the stream. They can also add comments or Like a photo (for which you'll get a notification), plus share photos with all of Photos's normal options (Facebook, Twitter, Email, iMessage, etc.) or save it to their Camera Roll. (Note that in iOS 6, the Share button doesn't appear until you tap Edit while viewing an album or photo stream.)

The one thing they can't do, however, is add their own photos to the stream. That's a disappointment, because it means that if I go on a trip with my family or friends and we want to pool our photos, we each have to create our own Photo Streams that we share with everyone else. (Or do the ritualistic memory-card exchange dance at the end of the trip.) I hope that Apple looks into adding this feature in a future update, since it would greatly improve the experience of sharing photos.

When you subscribe to a Photo Stream, it shows up automatically on all of your iOS devices.

You might wonder what your contacts will do should they be among the iOS-less. No problem: As mentioned above you can also create a Web-based Photo Stream for them to view in their browser, although they cannot comment on or Like pictures posted there.