I used to choose an iCloud Photo Stream of mine for my screen saver. But now, when I go to my screen saver settings, there is no option to choose an iCloud Photo Stream, but only Apple's default screen savers.
Any ideas about how to sort it out?
Please check this image below
If this is not visible on your Mac (I've had the same issue after upgrading to Mavericks) please logout iCloud entirely (remove everything from your Mac) and log back in.
It will be visible now.