Pikorski finds "Twitter's usage patterns are also very different from a typical on-line social network. A typical Twitter user contributes very rarely. Among Twitter users, the median number of lifetime tweets per user is one. This translates into over half of Twitter users tweeting less than once every 74 days." And there's some very intriguing stuff in this article on gender and Twitter.
Also, there's a piece at CNet on the lack of loyalty displayed by Twitter users towards the service, as compared to MySpace and Facebook: "Twitter Quitters Post Roadblock to Long-Term Growth" by David Martin, Vice President, Primary Research, Nielsen Online.
Martin writes, "Currently, more than 60 percent of U.S. Twitter users fail to return the following month, or in other words, Twitter’s audience retention rate, or the percentage of a given month’s users who come back the following month, is currently about 40 percent."
Curious stuff. I also was unaware that Twitter got a 100% boost from an Oprah mention, though the boost doesn't appear to be translating into repeat offenders.