Every morning I log into my machine, a nice Yahoo Widget shows me the weather of my city in a very nice manner. Today, It was drizzling and when I logged in, it showed me a nice photo of clouds and a five day forecast. When I logged into GMail today, I noticed that the theme was slightly different  than everyday. Was there any rain element previously in the theme? No. Gmail changed the themes slightly according to my weather. And made me smile :) Although this small feature is not a core functionality of an email system,  small tweaks like these make your day; they also differentiate mediocre products from refined ones. Features like these differentiated Apple's iPod with all other MP3 players in the market