For everyone that likes to customize a little more, I recommend the Safari Plug-In WasteNoTime. (There are similar plug-ins for other browsers). 

You can add stuff to a blacklist too, but allow yourself to use them for a specific amount of time everyday. You can allow yourself 30 minutes browsing of your blacklist per day and otherwise its blocked. You can also block the full access of the internet right away by pushing a button. To get the most out of it I let my girlfriend set up a password, so I cant even edit the settings anymore. Once my time of leisure browsing is over, I literally cant do anything that day to get back on blacklisted pages, unless I download and install a new browser.

This little plug-in has been one of the biggest productivity boosts I ever gained!

Cheers,
Florian

I do this periodically, usually for a month or so at a time. Like, right now I don't need it. Most days I don't check reddit, and I'll check HackerNews once a day and only read stuff that's directly applicable to SETT. But in times past I've gotten into that gross cycle of facebook > reddit > hackernews > twitter > facebook...

I love these sorts of blocking programs because they very quickly interrupt that habit/addiction. I've found that a month of it is enough to erase the patterns and allow me to operate on my own self control again.

Hi Sebastian, do you have any other suggestion on structural changes that can have massive impact in productivity of knowledge workers?.