Google announced today that it'll be instituting some changes to tailor the ads that appear in your inbox to your interests. Using the algorithmset up for Priority Inbox, Google can now better understand what is actually relevant to a user. The company is basically implementing the same technology used to sort your inbox for a more commercial (and probably more profitable) pursuit. For instance, if you get tons of bacn e-mails from travel websites but never read them, maybe travel ads aren't actually such a clever idea.
Even if you never click those ads in Gmail, the change will probably make for a somewhat more pleasant user experience. In my inbox right now there is an ad up for "The Most Authentic Biking & Hiking - Tours Of Italy Since 1989." That would be lovely if I were a 50-year-old millionaire, but frankly it just comes across as cruel.