[rayiner]

You're dancing around the heart of the issue, because none of your examples involve the bank looking at the contents. Google doesn't just "make some guesses about what might be in" your e-mail. It reads your e-mail to figure out what kind of ads to target to you. AT&T inspects your traffic to do traffic shaping. Facebook has full access to the contents of your profile. Numerous employees at all of these companies have access to the contents of your accounts, not just what's on the "outside."

Imagine if the bank had the lock to your lock box, and bank employees had access to the contents of your lock box, and bank employees regularly rifled through the contents of your lock box. Also, the bank had no obligations as to your lock box. You couldn't sue the bank if they lost the box, or if someone stole the contents, etc. To me, all that would make the box seem a lot less "private."

The 4th amendment doesn't extend to say the stuff you store in your friend's garage. Google, Facebook, etc, accounts resemble that a lot more than they resemble bank safe deposit boxes.

[nooneelse]

There is an important distinction to be made, though, between employees at Google having access to read the contents of emails and them being able to run text analysis on those contents for ad-able words and phrases (what I was trying to get at by having the bank-generated weight-log in the example). Most people know that Google does the latter, but it is dubious that many people at Google have access (especially the kind of unconstrained access connoted by the term "rifled" in your modification of the deposit box) to do the former.

Also, it is not like a friend's garage; they aren't hosting people's email as a favor. It is more like a rent-a-storage-room place with a peculiar method of paying the rent; there is a business relationship/transaction going on. We trade algorithmic-advertising access to our emails in exchange for them providing hosting.