If you really do need a network connection to do work I've found that the Leechblock plugin for firefox helps me regain at least some measure of control. You can set it to allow yourself a certain number of minutes per hour of "freedom" and the rest of the time it simply blocks the sites that you tell it to. It's amazing how many times per day I see that block page. (And at the moment, hacker news seems to have slipped through my filters :) https://addons.mozilla.org/en-US/firefox/addon/4476