Disconnecting Distraction is a small piece of writing by Paul Graham which anyone who works with a computer can identify with. His solution of having a "work pc" which isn't connected to the Internet isn't going to work for everyone, but thinking about the concept is definitely a good tool to use as a wake up tool.
And my main computer is now freed for work. If you try this trick, you'll probably be struck by how different it feels when your computer is disconnected from the Internet. It was alarming to me how foreign it felt to sit in front of a computer that could only be used for work, because that showed how much time I must have been wasting.
Wow. All I can do at this computer is work. Ok, I better work then.
My compromise when working at home is to have 2 PCs side by side (linked via Synergy for convenience). One of them is my main work rig, the other contains all my messaging software - MSN Messenger, my email, Twhirl, and whatever other FOTM thing I'm into at the time. If i need to concentrate I just flick off the second monitor, and I've instantly removed a lot of my distractions.