Modern web apps are continuing to increase in complexity and file size, and with that we need more graceful ways to load our content. Preloading animations to the rescue!
Another alternative is the Spin.js jQuery plugin by Felix Gnass (@fgnass). This one is a cute use of jQuery and CSS3 for a Mac-style spinning preloader with lots of parameters to tweak the shape and size. But for me, this is probably going overboard when a simple animated GIF or even a simpler use of only CSS3 would suffice.