You may have noticed recently that the news feed in the desktop/web version of Facebook uses a special placeholder graphic whilst it waits for content to load.
This is a nice bit of UI because it fulfils several functions; making sure the page isn’t blank whilst loading content and preparing the user for what will appear there. If you’ve seen it before, you’d notice that the lines of “content” actually animate with a flash that moves left to right like a traditional loading bar. They could have gone with just a standard blob that moves from left to right, but the speed of the flash and the colour treatment given help to imply something faster and higher-tech. When the content actually loads (which is quite quick on an i7/Chrome) it just replaces the preloader. I did think they could have used a fade here but fades in UIs tend to risk creating a perception of slowness and it seems what they were targeting here was “blink and you’ll miss it”.
Overall it’s a nice and subtle piece of functional design, and it certainly beats staring at the browser loading bar.