I think the effect of people being aware of HN would be quite different from that of HN being available whilst reddit wasn't. Essentially HN is not as 'good' at

I think the effect of people being aware of HN would be quite different from that of HN being available whilst reddit wasn't. Essentially HN is not as 'good' at doing what reddit does (because it's not meant to), so increased awareness isn't likely to shift people from reddit. Take away reddit and things change. It will be interesting to see the effect on the web without reddit for a day. With no serious Digg these days, HN would be high on the list of alternatives (even though it is not aimed as such), and there will no doubt be a lot of SOPA posting that day.