There will almost inevitably eventually be an enterprising district attorney who uses "The defendant's computer is configured to automatically prioritize his email by his interests. We obtained a warrant for, and received, the contents of the defendant's inbox. The subject line of his most important email of the day: Lurid Kiddie Porn."

It will probably be used against someone who actually has bona fide interest in child pornography. Probably.

After all, cache contents and network logs are used to help convict people all of the time. Most of them are factually guilty, but the legal system probably does not see eye to eye with technically inclined members of this audience as to whether cache contents mean that someone intended or attempted to view the cached content.

Without knowing anything detailed about how all this is implemented, it looks to be derived from nothing more than is stored in your inbox:

The text of the emails, and whether they are read and replied to.

As such it seems like strictly less information than you are requesting that they store.

In the presentation they say that it's partially based on what E-Mails you read. So they're tracking more than just the information in your inbox, they're also considering how you use your inbox through the GMail web interface.

The read/unread state of each email is obviously stored to construct the ui. That seems like data you are already asking them to store.

I'd be surprised if this kind of data wasn't already tracked.

Oh yes, Google has explicitly stated that they track stuff like this. I was just replying to the "it looks to be derived from nothing more than is stored in your inbox" comment by moultano. Which is obviously incorrect, and Google even states so in their introduction video.

It'd be interesting to what degree using GMail over IMAP v.s. over the GMail web interface affects the heuristics of this new feature.