Design your focus - Read better, work better, sleep better, X better.

For me it's about having on/off time. There's nothing wrong with scanning Facebook/twitter/HackerNews, but I find myself mindlessly going there, especially in times of frustration or when I'm stuck on something. Basically it weakens my ability to really focus on hard problems. For me the best solution is something like the stayfocusd chrome plugin. It simply makes you aware when you're on one if those sites.