[avar]

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.

[moultano]

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.

[robryan]

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

[avar]

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.