FWIW, I've found the Leechblock plugin (and probably many others like it) to be a great help. I'm only allowed on FB and similar time-sucking sites (HN not included....) after 9pm. But I think it ultimately doesn't help unless you acknowledge the problem, as they say in AA. You're going to find ways of circumventing plugins like that, for me they mostly help in curbing the 'reflex' of typing in facebook.com in the address field. For that, it's great.
Also curious to know how helpful the HN crowd finds Twitter for actual networking purposes.
Also curious to know how helpful the HN crowd finds Twitter for actual networking purposes.