We had this same problem, and found that the April install and configuration document leaves out this important part (which was included in previous documents):
Set Permissions on the User Information List
In order to correctly display the Podcaster web part, users will need to read from the user information list. By default they don’t have this
On the left navigation bar under
Groups, click All People.
Settings, List Settings.
Permissions for this List.
Domain Users to the list.
Restricted Read permission.
Uncheck the box to send them an email, and click the