Hiding files and folders is generally reserved for system files that you don't need to see. Reader Anonymous, however, uses it much more liberally, turning it into a way to stay focused on one project at a time.
For this tip to be really useful, you need a way to easily show and hide hidden files. In Windows, you can use AutoHotkey to toggle hidden files and and off with a keyboard shortcut. You can show and hide files in OS X, and turn that command into an Automator Service for quick toggling (and assign it a keyboard shortcut to it in System Preferences).
Update: It turns out hiding files in OS X isn't as easy as it used to be. You'll now need to install and run the Terminal command setfile, instructions for which can be found over at Mac OS X Hints.
The main idea is that you can hide less oft-used folders, which help you focus on a specific task and get to the necessary files more quickly:
I set up any folders that I don't want in my sight, but that I want to be there (like my public folder) to hide. - right-click it, go to properties and set it to hidden. I set it to just hide the folder, not the contents just for the sake of it.
Then, I just show all hidden files with my keyboard shortcut when I need access to it. This will enable you to remove some folders (and files) from your sight, but still keep them in your Dropbox or Documents folder. I'm a person who likes to have all his documents in a single folder. And as a student I have a lot of classes and a lot of different files.
This is useful for more than just hiding the annoying "Public" or "Sites" folders, too. If you, like Anonymous, keep all your documents in one folder, you may prefer to hide folders like "finance" that you only need to access every once in a while, and keep the folders of your main projects shown so you can quickly access them whenever you need to.
It seems like an extreme measure, but if you have a way to quickly toggle hidden files on and off, it's actually a pretty neat use of the feature we hadn't thought of before. How would you integrate this into your document organisation? Let us know in the comments.