Photo Stream will become much more useful in iOS 6, with the addition of shared photo streams. You will be able to press a “share” button to share select photos from the Photos app via iCloud. Users with iCloud on Macs or iOS devices will immediately get the photos in their Photos app or iPhoto. Shared photo streams can also be viewed on Apple TVs and don’t count against your iCloud storage!
You will receive notifications when photos are shared with you. To make it more interactive, you can now comment on photos and view others’ comments.
Don’t worry if your friends don’t use Apple devices, you can still share your photos! Photo Stream can create a shared Web album for use on all devices.