There's the comment by "AgentConundrum" who argues that any method of limiting access to an addiction such as HN can be circumvented -- the simple truth is that you can't outsmart yourself. However, I see it differently.
When I open a browser window and click the Reddit bookmark, it gives me an error. While I'm staring at that error message, my higher thought processes have a chance to kick in and argue about what to do next. I think, "Editing my hosts file would be an admission of defeat. I'm better than that."
It's like the "brush your teeth" diet. You know, the one where you brush your teeth after you've had enough to eat. Whenever you want to have a snack, you think, "I can't... I just brushed my teeth. Snacking would undo my progress with dental hygeine."
Both of these tricks are flat-out illogical. A hypothetical rational person would not be affected by these tricks. However, if you were a hypothetical rational person, you wouldn't need to change your behavior in the first place.
As for HN and such, I find my interest waxes and wanes. I definitely have days where it's a big distraction, particularly when I'm waiting 10 seconds for something to compile and come back ten minutes later. Then there are days when I'm too focused on coding, marketing or whatever I'm doing for it to be a big distraction.