Stuck with a piece of code that you want to figure out how to write in order to add that feature to your application? Get unstuck by tapping into the massive number of lines of code that have already been written by other developers all around the world. All you have to do is just use Google Code Search to look for a piece of code similar or identical to the one you want to write. You can even specify in which programming language you want the code to be!
The open source code has always been there, but the idea of instantly having access to any part of it and having Google pinpoint the exact piece of code you are looking for from among this enormous body of code is what makes the whole idea amazing. No need to reinvent the wheel anymore. Now that's what I call real usability of code.