Privacy: What details of a user's subscription list and post views are stored by Google?

I'm curious about what details are stored remotely by Google.

The existing subscription list is naturally associated with the user's
account, but, after a subscription is cancelled, does a record of that
past subscription remain? In other words, is it possible to determine
every subscription ever held by a user, whether currently subscribed or
not?

I'm sure starred posts are associated with an account, just as current
subscriptions, but are remote records created documenting all posts
actually viewed by a user?

I'm not a privacy nut, just a law school student testing the waters for
a possible paper topic. Today, requests are occassionally made on
libraries to reveal what books a person has checked out. At some
point, I expect those same requests will be made on Google for a
person's Reader subscriptions. But, Google's not quite a library and a
person's Reader subscriptions are not quite books. I'd like to measure
these differences against the law and precedents to see if I can figure
out what new issues may arise.