Why Did My iCloud Photos Appear... Then Disappear?
by David Murphy from Lifehacker on (#44H05)

As I've written previously, iCloud can be a little confusing. It's not meant to be-at least, I don't think Apple intended it to be-but a number of people seem to get caught up by iCloud's synchronization setup. While it's wonderfully convenient to have the same photos appear across all of your iCloud-using Apple"