After about a week, here are my results.
Using this plugin has forced me to notice that I have a bad work algorithm: when I hit a roadblock in coding or writing or whatever and I can't immediately see my way through it, I go to the Internet. The plugin basically halts this particular algorithm - when I try to use the Internet I get bored of waiting after about five seconds and go back to working, and usually figure out whatever the problem was.
I quickly realized that some discipline is still required. I have a smartphone, so I have to force myself not to simply use the smartphone for internet distraction. Additionally I convince myself that it would be shameful to find some other workaround like using my remote machine or one of my virtual machines.
Overall, I believe this made my workweek more productive. We'll see if I manage to work around my own convictions and find other ways of distracting myself.
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. :)