Capital_C - 5:51 pm on Dec 22, 2008 (gmt 0)

no, I don't believe its a subdirectory within the server. Google offers so many services, one server would become very crowded very fast.
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Setting up a cookie/session for each domain at login is an interesting idea. And I do believe I see some things similar to this happening.

What if I have 100 domains? I may not want to establish 100 sessions/cookies. Just allow the user into one of the other domains as they feel the need to hit those other domains.

The insights have been great. I've started calling what I'm asking for "multiple domain session" and googling that has yielded some results. I look forward to your help in clarifying this further.