Actually I think that article barely touches the surface… the data-sharing and analysis goes much deeper than that.
I have heard of programmers that were hired to do the sort of information tracking behind the targeted advertising on Amazon and such. The individual quit to work for 1/3 the pay because he viewed it as so incredibly immoral.
This involved tracking personal information through cookie trails (cross referencing cookies from many different companies), being paid to steal information from other companies databases, etc.
There is no doubt in my mind at all that google is harvesting every word of every email and tracking it between users to produce information for advertisers and marketing companies. But since this is happening with pretty much everything else anyway… just live with it and use gmail’s nice features. (It’s not like your emails don’t pass through other servers on their way to the destination no matter what service you use. For sure there are boxes out there that are reading them.)