I need some info about shared photo streams

http://www.apple.com/icloud/features/photo-stream.html

1000 of your latest photos. With you all the time.
iCloud manages your Photo Stream efficiently so you don’t run out of storage space on your iPhone, iPad, or iPod touch. If you have Photo Stream enabled on your iOS device, every single photo you take appears in a special Photo Stream album that holds your last 1000 photos. You can delete any photos you don’t want from the Photo Stream.1 To touch up a photo or keep a favorite shot permanently, simply save it to your Camera Roll. iCloud stores new photos for 30 days, so you have plenty of time to connect your iOS device to Wi-Fi and make sure you always have your most recent shots handy.