I have a SharePoint 2010 Foundation installation on Windows 2008 R2 and SQL Server 2008 and using Claims and Windows authentication.
Subsites are visible only to members of a certain group. However, when I add a user to the AD group that has access to a given subsite, the permissions for that user in SharePoint is not updated before the next day. So there is a mismatch between the permissions in AD and the ones in SharePoint.
For me, it seems like SharePoint is caching the permissions, and only updating them once every day. Is there a way to force a refresh so new permissions are loaded into SharePoint at once?