This may not be practical, but if the urge gets bad, take out your ethernet cord or wireless modem or whatever and put it somewhere really, really inconvenient. Put it in a bowl, fill it with water and freeze the sucker; lock it in the trunk of your car; etc. I haven't used the trick for gambling, but it works wonders when I have other, non-internet work needing to be completed (speaking of...time to go get that bowl of ice freezing...)
If it takes a little bit extra to get it, you'll probably wind up doing something else instead.