[_delirium]

I've noticed that also, but I suspect it's mostly how people use twitter, rather than the overall population of twitter users; i.e. black twitterers are more likely than white twitterers to post in large public hashtags as a sort of chatroom.

A study (http://www.pewinternet.org/Reports/2009/17-Twitter-and-Statu...) did find that 26% of blacks vs. 19% of whites use "Twitter or another status update service", but it also found a large correlation with age. Since black demographics skew younger than white demographics, my guess is that the 7% racial gap would disappear if you controlled for age.