With a retention rate around 40%, Twitter’s growth will certainly be limited in the long run.  Facebook and MySpace had retention rates nearly double of Twitter’s at similar times in their respective growths.  Even today, Facebook and MySpace have retention rates around 70%.

So, perhaps all those companies that are trying to capitalize on Twitter should take pause, and wait to see what the core Twitter audience will be.  If people are not staying with Twitter for long, the challenge will be to engage this audience and keep them engaged for more than a month.  Apparently, Ashton, Oprah, and others can bring a large audience, but unfortunately it also appears this audience is leaving very quickly.