If you knew at the start that that would happen, it might have stopped you from giving them -- originally and mostly through Gmail -- your contacts list. (Or using other affected services.) But when you signed up, they were all about "privacy" -- particularly after their previous efforts to reassure people in the face of concerns over automated ad targeting in Gmail. (Which was its own event, but I guess people generally decided that, as long as its purely automated and doesn't affect anything more than ad presentation, they could live with it.)

Hmm... as a thought exercise, what if your Gmail content starts affecting not just ad presentation but your search results. Would you have a bit more concern, then?

What if your employer starts examining employees' "customized" search results (perhaps by hiring a third party that specialized in this) and making inferences?

I assume they can and some may well already log and analyze the ads returned on those searches. Now that ads are starting to "follow people" across searches and sessions -- at least at some sites -- what personal habits might you inadvertently be bringing with you to work, via third parties' tracking of and response to your web use?