That's a good point, although the question is on HN and SD, what % of items do users actually click on? While HN has far more single news items, Slashdot has a lot of comments, and the articles themselves are longer. Apples & Oranges to be sure.
It varies widely I imagine- you can see it on Slashdot very obviously: some stories get 1k comments, others get 50. There is a HUGE variance in interest on stories- and it's not always predictable. But when the planets align, I bet the traffic generated could easily be low 6 figures to a single site, and that would be over 3-6 hours.
I created this account recently. I never posted during the original story that got picked up here (although I did read the comments). And yes, it's me. But you have no proof of that fact.
I created the account yesterday simply to share the story that Slashdot actually picked up. Then I emailed info@ here to try to get 'CmdrTaco' back. It sucks that someone is squatting my nick here!