When we dug into the updated Gmail app in the APK Teardown a few days ago, there was clear evidence of a system for displaying ads in the Promotions folder much like desktop Gmail. It didn't take Google long to start implementing them either – the first users are seeing ads right now.
These ads look like email messages, but the color is different and there is a badge marking it as an ad. Ads in the desktop Promotions folder look almost exactly the same. The APK Teardown also revealed a way to save or dismiss ads, but it's not clear if that is being used yet. If it is, we haven't seen a screenshot of it in action yet.
Keep in mind that these ads should only appear at the top of the Promotions folder in Gmail. If you don't use that folder, the ads should never invade your eyes.
[Android World (Dutch) – Thanks, Ruud and rmkilc]