Google announced on Google+ that you can now target your ads around those who make in-app purchases within the Google Play store.
The new option is a check box under the interests tab, that reads "only show ads to people who purchased an app or made an in-app purchase." Previously, Google only supported buying an app, but not the in-app purchases.
Here is a screen shot of the targeting feature:
Google said:
Today we’re announcing an enhancement for in-app display ad campaigns that enables app developers and marketers to show ads to people who have made in-app purchases through the Play Store. This is an addition to the Google Display Network feature we recently added that allows you to reach people who have previously purchased a paid app. These new settings can help you identify and create a campaign strategy around your most valuable customers.
Forum discussion at Google+.
