I get that -- even places not explicit aimed at exploiting addictive personalities and the easily distractible can end up becoming that kind of time suck. I'm not sure there's an easy solution, though.

Years ago, there was a browser game called Kingdom of Loathing (it looks like it still exists), and it tried to balance things by giving people a limited number of turns per day, so that people could have fun, but also not be sucked in 24/7.

And it failed, because people kept using every trick the game offered for extra turns, and then when they were done, they'd stick around the in-game chat, or buy/sell at the in-game mall, etc.

Basically, if a product is good (and I think any of us posting regularly agree that SN is good), it can also be distracting and even addictive.