Anybody know where the data for mysite Organization Browser is stored (the silverlight webpart)? We have a employee who left the company but he is still showing up in the Org Browser. He has been removed from AD. Do we need to delete his profile and mysite so that he is not the org browser anymore?
As Anders says, the information is coming from your User Profile Service Application.
After a user is removed from Active Directory, it is not removed from the User Profiles immediately. It is something like the second time it syncs. and doesn't see it that it goes from the UPA. This may be why you are still seeing this user in the Organization Browser.
It will be no surprise that the definitive source for this subject is Spence Harbar's blog.