Working on a computer can be very distracting. You are bombarded with a constant stream of email, RSS reeds, and other internet content. If you want an excuse to avoid work, your mac has a big one sitting there, just a click away, tempting you. Sometimes I have enough discipline to avoid that siren song. Other times, I don't. That is why I really like Freedom. It is like carrying a copy of your mom in your Mac always ready to make sure you get your work done. Freedom is a simple little application that turns off your internet tap for up to six hours.
Once you click "OK", that is it. The airport turns off and you are officially out of the distraction business. You can't get back online until the time elapses or you reboot your Mac. This is perfect when you really need to buckle down but don't trust yourself to avoid checking MacSparky just one more time.