Conditions for iOS - When pulling to refresh in Conditions, the progress indicator is a thermometer that fills up as you pull down.
/via Jake Marsh
Mac OSX - The world map displayed within the Data & Time system preference panel changes with the seasons.
/via John Blackburn
Vouchercodes- On the unsubscribe page the background & editor’s avatar turns from a blue (sunny day) background to a rainy day when unsubscribing from all newsletters.
Weather app - Swiping down in iOS 5’s weather app reveals hourly forecasts.
Google Mobile Weather - Background color changes according to the time of searching.