I'm the type of person who like's to have the bare minimum number of windows shown at a time. Whether it's Mail, Safari/Chrome, Twitter, or Reeder, I always like to have that be the only window that is visible on my desktop. To help that, I've written a little applescript that will help me focus on the task at hand:

tell application "Finder"
    set visible of every process whose frontmost is false to false
end tell

This script, combined with Alfred, lets me hide all other windows except for the one I'm currently focused on with a simple key combination.

Here's the script as an app: Hide Other Windows