Back in the time when I was working on jobs for Google (they were my employer's client), withgoogle.com was a domain where we hosted things like "über-doodles",

Back in the time when I was working on jobs for Google (they were my employer's client), withgoogle.com was a domain where we hosted things like "über-doodles", all the funky gizmos, etc. It's basically so that they don't run "experimental" / "untrusted" code in the same cookie domain as google.com; same thing goes for googleusercontent.com, where they store user-uploadable media. It was always my impression that coolproject.withgoogle.com is meant to be understood as "company X made a cool project with Google".