Everyone is talking about the 8% figure. 8% of Americans are on Twitter. Wow! Most people think that is a small number, to me, that is huge. I bet it doesn't compare with Facebook, but 8% of American's have used Twitter! That is big.
But they also say 21% of those Twitter users don't read content on Twitter. They may post content, but they do not read content. In a sense, it might be automated or just random tweets or they might not tweet at all. Either way, about a quarter of Twitter users don't really use Twitter. Almost half barely use Twitter - they check in every week or so, which is not the way to use Twitter - ask any Twitter user.
So I'd say probably 50% of the 8% really use Twitter. So maybe that number is closer to 4% of American's use Twitter. Maybe that number is more realistic.
Forum discussion at WebmasterWorld.