Twitter's rapid adoption is forcing change on the big guys. First, Twitter's success casuses Facebook to accelrate adoption of more features; today a report that Google is readying Twitter search.
What happens next? There are a myriad of possibilities for Twitter. While the business models for all of this remains unclear, the level of user activity has everyone's attention. This type of explosive change often attracts a round of over-investment in the gold rush phase (11,000+ Twitter apps already), but an eventual shaking-out as the winners emerge.