This feature is complex. We will be working very hard on this during the next few weeks.
Soon this ticket will contain information about how we are planning to implement this.
The idea is basically to let the user customize the interface as he wants, like the Google analytics dashboard or Netvibes.com
We are also trying to think of a way to use the widgets on other widget platforms such as Igoogle / netvibes / windows vista or the apple dashboard.
Any idea or suggestion is more than welcome.
Thanks to julien hard work this feature is now implemented! Hourra! http://piwik.org/demo