We have an iPhone app available in the app store that utilizes push notifications. Normally we use this functionality to inform users when new podcasts are available (usually once a week).
We've noticed that a significant portion of our users are not updating as regularly as we'd like (26% haven't updated to the latest version from the app store which was released 17 days ago).
We're considering using the push notifications to alert users of the availability of an update in the future but we can't retroactively differentiate between those who have upgraded and those who haven't (meaning even those who have updated will receive the notification). In the future, of course, we'll add the functionality to only alert those who have upgraded.
Do you think sending a push notification now provides a poor user experience or could be confusing to those who have already updated? Do you think it's worth alerting everyone to inform the minority percentage that hasn't been updated?