Deep dive: Aperture and Photo Stream, how do they work? | TUAW - The Unofficial Apple Weblog
Some detailed information on how Aperture and Photo Stream work together. For example, I recently wondered how RAW files are handled:
According to the Aperture documentation, how RAW interacts with Photo Stream isn’t immediately obvious — but it is very important that you understand it. If you send a RAW file from Aperture to Photo Stream — either automatically via the “import all” checkbox, or manually — and if that RAW file has no edits applied, then it’s the full-sized original RAW that ends up in Photo Stream. On the other hand, if it has had edits applied then Photo Stream ends up holding a JPG copy instead.