"In gmail, google reading my email tells them to sell me product x and we think that's the end of it." I don't want to put on a tin-foil beret, but how much re

"In gmail, google reading my email tells them to sell me product x and we think that's the end of it." I don't want to put on a tin-foil beret, but how much revenue do they actually make from ad-words on the side of GMail? I can't imagine it's much, but then I'm probably biased in that I don't even notice they're there. The pragmatic part of me realizes GMail is a service that improves 'lock-in' to the 'Google Ecosystem'... the paranoid part of me thinks about how valuable a "search everyone's inbox" rather than a "search my inbox" feature would be.