I've just switched the LeechBlock Firefox extension because you can delay the page loading (thus making you think why you went there in the first place).
Yes! A 10-second delay is enough to make me think, "Do I really want to spend time on this?" But not enough to make me circumvent the filter. I also really like its lockdown mode, so that I can say, "For the next 2 hours, no distractions."
