Safari: We've seen a few extensions that block time-wasting sites for Chrome and Firefox, but if you're a Safari user you haven't had too many options. Mindful Browsing is a browser extension that makes blocking time-sinks easy in Safari.
Much like StayFocusd for Chrome and LeechBlock for Firefox, Mindful Browsing allows you to click one button to block a site. Then, when you try and visit the site again, you're locked out for at least a few seconds until you get temporary access. Just like the other extensions, it doesn't take much to circumvent Mindful Browsing, but it hopefully is enough to break the habit of passively browsing time-sink web sites.
Mindful Browsing | via Minimal Mac