I think concepts like akrasia and hyperbolic discounting contribute somewhere in this approach too. If you can just make it through the initial rush of pleasure seeking behaviour and desire for distraction without acting on it, it seems to be much easier to re-focus on an less stimulating task.
Perhaps this is already well known, but it occurred to me yesterday and I thought I'd share it. The Internet seems particularly virulent as a form of procrastination; indeed, if, say, chatting at watercoolers took up as much time in the average office worker's day, we wouldn't make jokes about it. What is the feature that makes it so deadly? I suggest that it is the random reinforcement schedule: Every five minutes you "press the lever", that is, check forum X or site Y. And every six or seven checks you get the reward: Someone posted something interesting! This random reinforcement is ideal for creating addiction; thus, for example, slot machines.
As a way to avoid this effect, I'm going to strive not to do anything on the interwebs except at precisely defined times, or unless I have a specific goal in mind, say "Look up this method signature". Wish me luck, or better still, wish me willpower. :)