If a site has been using Google Analytics for a while and someone wants to drill in and see data on individual sessions, how would you go about doing getting that data? Is it even possible?
Its against Google's TOS to track by inddividual session. You can add custom variables per user, and track that way. But they are more intended for grouping, and if google finds out you are tracking per user, they may cancel your account.
Last you can host your own visitor tracking script, although its a bit pointless unless the data is critical to you.
One good practice is to write internal code to track important actions of your registered users. That way you can track in your own DB the interactions that matter to you, and use that data in your app.