I understand that the iOS 5 Photo Stream is a collection of all of the recent photos taken on all iOS 5 devices in a given account, synced with those devices through the cloud. It is not clear to me, however, what the Photo Stream settings in Aperture do.
It appears that "Enable Photo Stream" simply connects Aperture to the Photo Stream and makes it available as a source for viewing and importing into Aperture; but it is not clear to me what "Automatic Import" and "Automatic Upload" do.