Yesterday version 1.2 was released with a range of new methods and properties for dynamically updating the charts after render time. Monitor a server variable over time using Ajax, or let your users modify the data.
series.addPoint() are only a few of the new tools available for modifying the charts after render time. Check out the new methods under “Methods and Properties” in the API reference. Or see the examples showing a live updating chart, a chart where your users supply the data, or a chart with a master-detail type navigation.