British Gas - iPhone app has a button to turn on the camera light when submitting a meter reading.
/via Jaik Dean
Google Maps iOS - Shaking the device allows the user to submit feedback.
iOS 6 - When selecting new wallpaper, preview screenshots show a realtime view of your current home & lock screens
/via Rich Cornish
Tweetbot - When replying to a tweet, swipe down to see the original tweet and author.
/via Kevin S.
Facebook Camera - After clicking the install now button, a pop-up message offers to text you a direct link to the app, with your phone number pre-filled in.
/via Taylor McKnight
iOS - If you tap the camera icon in the lock screen of iOS 5.1, it bounces up to encourage you to slide.