For example, if you've recently read a lot of messages about cameras, maybe you'd like to see an offer from your local camera shop. On the other hand, if you've reported these messages as spam, or marked them 'not important' you might not want to see that offer. Soon, some of you will start seeing fewer ads overall, and focused on subjects we hope will be important to you, at the right time.
Unlike Google Search, you can disable personalized ads from Gmail's settings page. Just make sure that this option is not checked: "Show more useful ads by using importance signals from across my messages".
"Only a few users will notice the change to begin with, but as we improve it we'll roll it out more widely. As always, ads in Gmail are fully automated - no humans read your messages - and no messages or personally identifiable information about you is shared with advertisers. We've already cut down the number of ads shown per Gmail user by more than a third, and we hope these signals will enable us to continue to show fewer, better ads in Gmail," explains Google.
Google also tests a new ad format that includes offers and coupons for your local area, which might be related to Google Offers, a service that will compete with Groupon.