The scrolling in the new Gmail theme preview was acting all broke this morning, so I went up to the little gear to change the theme back to an old one—and then I saw this.
It's a new option to "Switch friends to Gmail" that's all up in my mail settings, launched in conjunction with Google's twee ad campaign to get people to switch to Gmail (clicking it takes you to Google's Email Intervention site). Which I don't dislike quite as much as Mat, though I feel like the campaign's maybe out the door 5 years too late? (Unless you consider the real aim is probably to get people to join Google+.)
Anyway. I know Gmail is free and all. And it's great. In fact, I've told lots of people to switch to Gmail! I don't need another a reminder. Especially not in my goddamn mail settings.