The key to twitter's success, is tying it in with networks like facebook. The market for these sort of social tools is becoming crowded, so they either have to be pure simple genius enabling the masses or a hardcore niche audience, and ideally able to work with existing networks and environments.
BBC's Rory Cellan-Jones writes:
But I'm not convinced that Twitter is really going to spread in the way Facebook did, beyond the digerati into millions of people's lives. What's more, I'm struggling to understand the business model.
Making a reasonably successful tool a revenue winner can be key to its lifespan, but there's not much to twitter, so adding commercial twits might start to turn off users?
Twitter works for some people, others don't get it or feel the need to document their life, which is why not everyone in the world keeps a written diary.
Not sure if twitter will grow in the same way as facebook, but its got a decent chance now it can be integrated.