With 1TB free at flickr why use google or dropbox for storage?
You are right. Didn't realize Flickr offered the 'never-ending camera roll' functionality for iOS as well. At 1TB, that seems like a pretty good solution for those short on Dropbox space.
Apple really missed the boat by not having any of this functionality built in with the native Camera Roll + iCloud. iCloud only mirrors the photos that are physically on your device.
The Photostream feature that syncs 1000 recent photos is just a cluster. That should be relegated for creating shared albums only.