> they could even make ad targeting work by moving their mail-reading bots to the client Gmail ad targeting isn't a bit of JavaScript that can run in real time

> they could even make ad targeting work by moving their mail-reading bots to the client Gmail ad targeting isn't a bit of JavaScript that can run in real time in the background. It's a series of huge map reduces touching data sets larger than any client computer could store. Just indexing a pre-prepared list of mothership ads would result in a horrible user experience (far poorer ad targeting). Google has a vested interest in only showing you ads you might be interested in; it doesn't work as well as it should, but it works magnitudes better than the state of the art 10 years ago.