From the team on Kickstarter:
In terms of our schedule, we’re sticking pretty closely to an aggressive timetable we put together at the end of May (remember our first timetable was created before we launched on Kickstarter, when we were expecting to manufacture just 1,000 Pebbles). While we won’t be able to start shipping Pebbles in September, our current schedule has us on track to go from manufacturing zero to 15,000 Pebbles per week as soon as possible.
Too bad for those who ordered one, but understandable given the unprecedented demand.